I'm somewhat sympathetic to that idea (I haven't felt guilty about being straightish, but I've wished I were more bisexual once in a while, and succeeded in pushing myself in that direction in some cases), but I'm curious now: is gender the only dimension you'd apply that to? Would you also take a pill (again assuming it's really really safe) that would make all outward physical attributes irrelevant to how attractive you find someone? Would you take a pill that would make you enjoy every non-harmful sexual practice/fetish (not necessarily seeking them out, but able to enjoy it if a partner initiated it)?

(I originally started writing this comment thinking something like "hmm, I'd take the bi-pill, but let's take that reasoning to its vaguely-logical conclusion and see if it's still palatable", but now I'm actually thinking I'd probably take both of those pills too.)