Speaking as a woman, "being a man and putting your foot down" DEFINITELY isn't going to help. In fact, it'll solidify our position even more. And we can make your life a living hell if so motivated... ain't that right, ladies?

My advice, not knowing your wife, is to debunk all her fears. If she's worried about the snake escaping, prove you'll make the enclosure escape-proof. If she's just unfamiliar with snakes, take her around them BEFORE you buy one and let her find out for herself how sweet and fun they can be. Destroy each and every one of her reasons to say no and she'll be left with no good reason to object. Definitely try to come up with a compromise, that's what marriage is all about, right?