It's one thing to use these kinds of pronouns for yourself, or referring to people you know personally or feel connected to. It's a whole different ball park to claim or push for that everyone should use them regularly, or that the news media, schools, courts and academy should be using them as a default. I would agree with what Darkling said in another thread (on the liege board) that physical sex, social/styled gender and 'sex' (as in 'the ways and parts you bring into play for sexual pleasure') are different planes and don't need to square, but to most people those three - and especially bio sex and social/behaviour styled gender - are so close they are never really separate. And in that kind of world, pushing for a single genderless pronoun will come out as an effort to declare "gender doesn't exist" meaning sexual and social gender differences do not really exist, or shouldn't exist: they are just free choices or arbitrary whims flying through the air and landing in somebody's mind. Unfortunately, a vociferous part of the folks pushing for a genderless pronoun in my neck of the woods, Sweden, do seem motivated by that kind of ideological motive: they want to drive the notion that gender is nonexistent and that any concept of definite, lasting gender is a means of oppression - but they only half own up to that motive.
I would agree with Ephiral that most trans people (also, most lesbians and bi people I know or have heard of) are *not* committed to saying 'social gender - gendered behaviour, styling, clothing, ways of acting and talking - is trash, it's arbitrary and can be changed or remixed within a relationship at the drop of a hat'. Recognizing the right to fit within a gender (including intersexed or 'non-standard' gender) that might not square with what you were born with is much more important than trying to wipe out anything and everything that references gender or bio sex.