Even if we regard it as a sliding scale, there's lesbian on one end, straight on the other, and bi for everything in between. That's why there's "bi, but leaning toward men" and "bi, leaning toward women". If you're taking dick, you exit the lesbian point and go on the bi scale.
You see, this is exactly the point which I'm not prepared to assume. I'm ready to accept it, if I find the arguments compelling, which I haven't yet, but I'm not ready to assume it.
It's obvious that the classification of bisexual must include gradation. There must be room for varying levels of heterosexual and homosexual activity and attraction within the bisexual classification. But it's less obvious whether or not the classifications of heterosexual and homosexual must exclude any and all activity of the opposite sort. In other words, I'm saying that there's a question as to whether or not every person who claims to be one or the other must be exclusively so, in order for us to take the claim seriously. You may not acknowledge the question, but other people do. Until all of those people accept you as the final arbiter on this point, the question persists.
Perhaps one reason why I'm more willing than you are to consider this as an open question is that I have a longer historical view of the issue. I don't know that this is true, but it may be. Let me point out, for example, that the use of the term "lesbian" to describe a woman who is exclusively homosexual is something which has only come about in the last forty years. As recently as the 1970s, the term lesbian was applied to any and all homosexual conduct between women, whether or not those women also had heterosexual interests. A woman who had a husband and regularly engaged in straight sex might still be referred to as a lesbian, so long as she engaged in any amount of homosexual conduct. Just like there was a time when men who were almost exclusively straight would still be described as homosexuals, if they had any homosexual involvement.
These terms have been in flux, and have seen subjective application, ever since they came into existence. It might be that the term "lesbian" has had a rigid definition for you and all of your acquaintances for all of your life, but I assure you that, in other times, and even for other people in this time, it's been less rigidly defined.
Using those women-leaning bisexuals who get dick from time to time while claiming to be "lesbians" to invalidate lesbianism (oh, so you people do like dick, blah blah blah) is an old tactic.
Invalidate lesbianism? What exactly does that mean?
I guess I'll proceed on the assumption that you mean "invalidate the concept that some women are exclusively homosexual," until you explain it differently.
Sure, I can imagine that some people, who are offended by the concept of exclusive homosexuality, might use something like a non-exclusively homosexual lesbian as a basis for a verbal attack on the idea. But the existence of a non-exclusively homosexual lesbian doesn't invalidate the concept of exclusive homosexuality, anymore than those people's verbal attacks invalidate anything at all. So I don't see this argument as a compelling reason to reject the validity of a claim to non-exclusive lesbianism, particularly given the historical context of the word.
If they're fucking around with guys, then their claim to lesbianism is laughable.
So you say. They say differently. And why should you be allowed to decide for them?
I'll say it for the third time in this thread (or maybe the fourth?). I'm in favor of terms having clear and concise definitions. And I'm in favor of uniform applications of definitions. But most terms actually have multiple definitions, or have ambiguity in their definitions. And I'm not in favor of arbitrary decrees, deciding that this one definition must be accepted and all others rejected. I won't have my use of language dictated to me or decided by fiat.
They just want some identity cred.
The concept of "identity cred" is a problem, in and of itself. But that's not what we were discussing, so I'll leave that one alone for now.