Because it outlines a hypocrisy in that particular type of feminism. The goal is to bring about gender equality, but it must be done by focusing exclusively on the problems women face. Supposedly women are so severely disenfranchised that there's no time to consider the underlying processes, which affect both genders.
I'm open to arguments which explain how men are tricked into sexist thinking, instead of lazily painting us as "entitled" and "the enemy". Which I think is most serious feminists, but they often get drowned out (particularly in certain online communities) by simpler, more vitriolic "arguments".
your definition of feminism is wrong from the start, therefore your analysis is inherently flawed.
We are all part of the patriarchy (or kyriarchy, which is what I've started using because it encompasses more than male dominance,) we all end up promoting it in one way or another, unintentionally or otherwise. The trick is to fight it and oppose it whenever possible.
It's why Lean In is more a problem than a solution. It maintains the status quo of the kyriarchy, instead of trying to rewire things to rid ourselves of the problem.
The system is inherently broken.
But more to the point, feminism doesn't actually just focus on women's issues, it focuses on race, and sexuality and class status, and a whole host of other things which I wish people would research enough to realize before making statements like this.
The point of the comic, however, is that this whole "let's call it humanism" argument denies the very specific problems that each minority (in the power structure, though yes the majority of the world is women,) faces. It allows the dominant members to grab focus for their issues, and continue to lead and direct the discussion as they see fit, when it needs to be the oppressed that lead the discussion.