What exactly is he saying, here? That people who do not accept/endorse homosexuality (homosexuals are 2-3% of the population in North America) are bigots? Really?
Short answer: yes, if.
Longer answer: As Arroz mentioned, you don't need to "endorse" homosexuality, per se. However, the contemporary viewpoint does seem to be that people "need" to accept them - "need" here being understood as being "meeting the minimum requirement for acting in a morally acceptable manner."
Likewise, the understanding of what it means to be "accepting" of homosexuality is largely defined as not having a problem with people who identify that way (e.g. a "live and let live" attitude), and as an extension of that, finding no merit in any particular set of restrictions or taboos that cite homosexual behavior specifically, or otherwise disallow homosexuals from engaging in society in any manner that heterosexuals can.
In other words, you don't need to care very much about the issue of, for example, gay marriage to not be considered a bigot...but you do need to be against laws that are against gay marriage.
It's also worth noting that the statistics regarding how much of the population are homosexual are highly in dispute, do to issues of self-identification as being homosexual, and self-reporting on such surveys.
As I was looking through the PHB at my local bookstore, I noticed that almost all the race illustrations were women. Likewise, it was my impression was that the same was true of the character class illustrations -- seemed to be mostly women represented. Is this a coincidence, or a result of having a female art team?
There's no way of knowing.
Knowing the answer to that question would involve not only interviewing the entire art team, but in necessarily being totally certain that their answers were true, which is - strictly speaking - not possible. The intent of, and influences on, the artist(s) are not something that can be communicated to the audience with total certainty.
On a tangential note, I will say that I think the idea of an all-female art team goes back to Zak S's idea that artist's should not be faulted for drawing what (presumably) appeals to them personally - the issue is that (if we presume that there are issues with the diversity found in artwork), a more diverse pool of artists need to be drawn from.
It's clear that Mearls is attempting to do so; the idea of going for an all-female team is meant to be a break from the larger set of contemporary/historical practices of all-/largely-male art teams. In this regard, I don't think that it's the start of any sort of anti-male trend, so much as it is an indication of the fact that, when things start to change, the pendulum will swing to the other extreme (and back again) before finding the center.
This all rubbed me the wrong way.
I share your concerns, insofar as I think there's an undercurrent of "if you're against this, then you're a bad person," but only to a limited extent.
More specifically, while I find merit with the attitudes Mearls is displaying with regards to the real world - e.g. how laws, corporate policies, and social expectations are set - I don't hold that the same level of thinking applies to fiction and artwork. That said, it's a moot point here, since what's under discussion are aspects of the real world (those being attitudes towards homosexuals, and who is hired to draw the art), so I'm fine with what Mearls is doing here (though I'm giving him the benefit of the doubt that the all-female art team isn't meant to be a new policy in place for WotC for all of its future projects).