Do you know why he's so adamant about you not getting a snake? I think that its important to understand this. Is it a phobia? A concern regarding money? A worry that he'd end up looking after it? Just a lack of interest? In my opinion, some of these reasons hold more water then others so it would depend on which one it was.
If its budgetary then he may have a point. Something you guys need to talk about. Maybe you can cut back on some of the other things you do to allow for the costs of a snake.
If its caretaking, then as other people said, you need to ensure him that you'd be the primary caregiver. Have you had a history of animals where he had to pick up the slack? Have you not accounted for vacation coverage? Try and address his concerns and offer him some guarantees.
If its personal like a phobia or a plain lack of interest, then maybe these folks here who are saying go for it are right. Unless there is a functional reason why a person doesn't agree with another person's hobby, they really shouldn't try and impede the process. Still, anything you do that you know will particularily bother him will generate consequences. Are you prepared to live with those consequences? How will they effect your relationship which ultimately should be the most important thing here.
I guess i'm coming at it from the point of view that no person is inherently mean and that he feels the way he does for a reason. Some times it takes a spouse to reign us in a bit if were not thinking things through completely. Of course, were all human so maybe he's working through some phobias or responsibility issues. Either way, you're a team. You're sharing stock so to speak. You guys should be able to compromise your way out of this clash of titans. I think communication is key here and I hope you're able to come to a sound agreement suitable to both of you.
*throws two pennies on the table*