Animal rights questions

Though I'm hoping to attend this Wednesday's Debate at Lolita, "Should Humans Radically Decrease Their Exploitation of Animals?," a tight schedule this week makes that uncertain. Also uncertain is which way I'd vote. In any event, I hope the debaters (particularly the yes debater) will address the question of what (if anything) would justify some exploitation of animals. In speaking to vegan friends, I find they often resort to arguments that some or another use of animals carries no significant benefits (that animal research is unreliable for developing cures for humans; that meat is unnecessary or undesirable as part of a human diet). That makes me wonder: Are they implicitly conceding that if, say, some experiments on rats would save numerous children with leukemia, the experiments would be justified? Or do they think (as I suspect many vegans do) that the experiments would be reprehensible regardless of results? And is the opposition to eating meat dependent on the supposition that meat has no health benefits (and should the fact that people enjoy eating meat carry any weight in the calculus)?