I think this strip also shows the way that many women reinforce gender roles in men.
Panel two: Women only want 'manly men'.
This is not just a stereotype: there is a lot of truth in it.
It's not true that all women are attracted to ultra-manly Schwarzennegger/Rambo types, and it's a massive oversimplification to say that women want "jerks," but women do tend to be attracted to men with more masculine traits than they have themselves.
Consequently, men have an incentive to display those traits if they want any kind of sex/relationships with women.
I have various flavors of reaction to this comment.
The first set of reactions are pretty knee-jerk: First of all, "sex/relationships" is sorta telling--it makes palecast's point out to sound like, "Well, if men want to get laid..." Secondly, "women do tend to be attracted to men with more masculine traits than they have themselves" is such a gross over generalization (on several fronts) that it doesn't add a lot to the conversation--as stated, it's sort of tautological (i.e. [straight] women are attracted to people who are men). At the same time, there are also so many exceptions to it in my own experience, that I want to put the burden of proof back on palecast to prove it.
On the other hand, I have a set of reactions that are less knee-jerk. Most importantly, I think it can be important for us to recognize the ways in which all of us reinforce traditional gender roles.
An Existentialist Aside
I get into trouble sometimes in feminist circles because I'm a big Simone de Beauvoir fan. One of the things that Beauvoir gets criticized for by some feminists is that she places a good deal of responsibility for the oppression of women on women themselves; this comes from Beauvoir's existentialist roots--at bottom we all have existentialist freedom, so in some sense of 'freedom', Beauvoir believes we are all ultimately individually responsible. But her philosophy isn't that simple, because she (unlike Sartre, as I understand it all) introduces the concept of practical freedom, and she shows that political freedom can limit us no matter how much 'existential' freedom we have. One example she gives is of a woman who is held against her will in a 'harem'--sure, she has existentialist freedom; she may choose to live that life or to kill herself, for instance, but she's limited to those choices by her lack of practical freedom, and Beauvoir wants it clear that this lack of freedom is important.
Back to Responsibility for Reinforcing Gender Roles
I mention all of this because I think there is some truth in palecast's observation--but I think that we need to tread very, very carefully when talking about it, mostly because it's complex stuff, but also because it's way, way too easy as men to slip into the "women like jerks" mentality. I'm pretty sure that conceptions of responsibility are usually more complex than people seem to think, which is why I brought up Beauvoir, and the way in which she is sometimes oversimplified.
For example, let's take the idea that women reinforce male gender roles by 'wanting manly men'. I do think it would be silly/wrong to deny this altogether. All of the millions of 'nice guy'(tm) discussions that are to be found on the internets aside, lots of men and women have had experiences in the dating world such that traditional male gender roles have been encouraged by both men and women. Regarding straight-identified people and dating (for the moment, let's limit it to this group of people, though of course traditional gender reinforcement can be found in interactions between people who don't identify as straight): what is going on when a woman says she wants a manly man, or when a man says he wants a womanly woman?
Well, first of all, such things mean different things for different people. Some women who say this mean they like men who look like lumberjacks (hi molly!). Some mean that they like men who take responsibility for their own well-being. Some mean that they like men who don't live with their parents any longer. And on and on. And it's important to remember that lots of women who may say this haven't critically examined exactly what they do mean by it (just as many men haven't critically examined their thoughts around liking femme-ish women)--and I would claim that these women may account for the majority of cases where things like "I like manly men" are uttered by straight-identifying women.
I would further claim that those women have some responsibility for examining what they mean by it. This is the main sense in which I agree with Palecast's comment: It's important to realize that men don't perform their genders in a vacuum, but in part as a reaction to women and other men.
But I would also claim that many, many women--most of the women I interact with on a daily basis and certainly lots of the women I've been romantically interested in--have thought at length about what they mean by "I like manly men" (if they do), and one thing these women don't mean is: "I like men who reinforce patriarchy." Rather, they mean that they like men who look like, say, lumberjacks, or men who aren't afraid to show their emotions, or men who don't feel the need to bully others, etc.
My point, which doesn't exactly run counter to what palecast has said, but has a different spirit, I think, is that we ought not treat masculinity as if it were a simple concept, easily understood by all. So, if it is the case that some women are sometimes encouraging traditional masculinity, we (men, women and others) need to try to better understand what traditional masculinity consists in, and what 'modern' masculinity might consist in. And, in a lot of ways, men have much more control and power over how masculinity develops than women have, though I'm not comfortable saying that women have no say in it, because of course they do.
Part of why the whole "women like jerks" mentality is easy to slip into is that men can have this "if we want to have relationships with women, we have to be masculine" mentality, which really is part of several false dichotomies. As I've pointed out, 'masculine' means different things to different people, first of all. But also, on a more personal level, do [straight] men really want to change the way they are (if they aren't masculine in various ways) in order to find romance with women? So, we end up with needing to continually define what masculine means (and people of all genders help to define this), but we also make decisions about how we want our identities to play out...and frankly it doesn't seem practical to 'act more masculine' just to find love, or even to get laid, especially given that 'masculine' means different things to different people.
So, what responsibilities to men have in perpetuating traditional masculinities? Well, first of all, they may put being themselves (like pig on the motorized horse) ahead of finding love (and/or sex) with people who don't like who they are. Men can work on what masculinity means to them, and what it ought to mean to them. Men can talk with other men about this, and with women, and find some differences of opinion and perhaps some comon ground. And this is just off the top of my head.
What can women do to stop perpetuating traditional masculinities? They can be conscious of what they mean by 'masculine' (and many women are conscious of this). They can ask themselves what masculinity does mean, and what it ought to mean.
But I still think that the majority of the work here can be done by men. Women may have some indirect 'control' of masculinity of men through relationships with men, but men can both encourage women to better understand masculinity, and walk away from women (and other men!) who don't care to look more deeply into what modern masculinity is, and what it might be.