This doesn't have to deal with "liberals", but rather a tiny minority of GLBT hardcores who, likely due to the horrible treatment and discrimination they've faced, have radical views on the subject that don't always serve their cause. There's a minority that tries to "out" people they think are gay, and feel that celebrities that are gay and in the closet are basically harming the gay population by not using their social standing or being honest with their fans - Queen Latifa and her "Personal Trainer" kinda thing.
As we can see from even this thread, there is still a lot of prejudice against GLBTQ individuals, and thus there's a dialog in the entertainment and public industry, to ensure that heterosexual relationships aren't the only ones considered "normal" in media. I'm all for this, in that the American sitcom "Modern Family" for example. I also support campaigns like George Takei's that provide emotional support and counseling to GLBT youth to deal with things like coming out, getting away from abusive families and environments, bullying etc. It is important to realize that even 10 years ago the "average" perception of GLBT and how society interacted with them was very different. Look up "Matthew Shepard" for one of the biggest example of literal "Gay Bashing" - his death helped spark the passages of laws to protect gays from violence.
For all this, I don't agree with assertion that Bert and Ernie are supposed to be gay. Yes, there's quite a few ways to interpret their behavior, as it has been popular to lampoon, but that doesn't mean they were written as homosexual and I don't see any real additional benefit in making them so. With that in mind, since Sesame Street undertakes the very worthy task of explaining difficult or confusing things that a child can be exposed to (ie. Death of a relative), there's no reason why there can't be some content including openly gay individuals. For instance, if there are straight married couples that visit Sesame Street and hold hands, there's no reason that there can't be a gay guest couple as well.
When the kids see that the puppets don't react any differently to the gay characters then they do the straight characters, it enforces the right idea that you don't need to treat someone different just because they're GLBT. As if I recall correctly, guest humans typically bring some sort of special information or job to the table, this has the additional benefit of showing that being GLBT isn't the only thing that defines those guests - they're also doctors, nurses, architects, physicists etc.
This path I see as much more beneficial to the GLBT community than simply making Bert and Ernie's sexuality an issue.
