If I'm reading about werewolves, I've already happily left suspension of disbelief behind! I've only read about one genetic "werewolf" that I can recall - Taura from the Vorkosigan series (not an actual transforming werewolf, just referred to as such) - and it was plausible enough, but I think a pseudoscientific explanation for werewolf transformation might hurt my suspension of disbelief more than a magical one, just because we already know some of the ways in which science works and getting it wrong would just be jarring. Of course, depends on how it's presented and how well it's written. (Yeah, I have trouble watching Star Trek sometimes. Suspension of disbelief is a difficult skill sometimes, but still totally worth it.)

Assuming a transformation takes place magically, it still bugs me if, say, a pregnant woman can transform into a dragon and back without affecting her pregnancy. NO it shouldn't WORK... even if it's magic.