"Easily"? You say that as if people with Luffy's level of poison immunity are a dime a dozen. And frankly, I strongly feel that this theory's positives far outweigh the negatives for a number of reasons, which include, but is not limited to:
-A chance for Chopper to further advance his medical skills (let's not forget his dream, now).
-If Law helps Chopper make the vaccine, it would further prove just how effective a pirate alliance can be, and could further convince Kid to form one with Apoo and Hawkins.
-The fact that the Straw-Hats had a hand in creating a cure for a deadly bio-weapon would give them another huge boost for their reputation (and don't forget, we already have several witnesses like Law and the G5 marines, and that's not even counting the NW pirates watching the events via TV broadcast).
-Kinemon would be further indebted to them for saving his life, in addition to finding Momo. And really, I'd think gaining favor with a powerful Wano samurai would in itself be a great benefit.
And as far as undermining Caesar's ability goes..... well, we ARE kind of talking about an evil piece of filth who'd gladly drug innocent kids for the sake of his experiments, so forgive me if I don't feel much (if any) sympathy towards him.
