It can be, yes. Plenty of younger people prefer it because for them it indicates a questioning aspect which is particularly helpful when you're exploring these things without pressure.
Personally, I don't like it, I don't use it as an umbrella, but I've had to accept that a decent amount of my fellow homosexuals use it for reasons that are perfectly reasonable.
As to the objection that some people use it when they're not, I'm not entirely sure what relevance that has for never using it at all in official settings, which is what the LGB Alliance campaign seems to be focused on.
Both lesbian and bisexual are self-determined. There can be lesbians who came out in later life, there can be lesbians who realise they're bisexual, heck, some well known GC campaigners are known for being political lesbians who chose to eschew relationships with men even if they may have felt attraction at one point. I doubt any of you would require a grading system for someone to use the word lesbian, beyond the accepted view here that it cannot be used by a trans woman. You'd just take them at their word if they said they use lesbian to describe their sexual orientation towards women.
So I don't really see why a lesbian, gay or bi person preferring the term queer is the rubicon which cannot be crossed because there might be someone who uses it who isn't in good faith. The UK law regarding orientation says homosexual, bisexual and heterosexual. But LGB is the shortened acronym, not HB. So you're already conceding that folk can use words that have a slightly looser application than that. This is why the arbitrary designation of the Q word as the big problem seems like bad faith outside of GC settings.