I think Apple made it clear that jailbreaking is up to you but things will not work the way they were intended to after that.
It's same thing if you buy customized third party parts for any car, the car manufacturer will not repair any damage. It's legal, but you're on your own.
Actually it's not like that. It's more like, you bought customized third party parts for you car, but the car manufacturer put in a little check to see that if you have any 3rd party parts, it will automatically break your engine until you take those parts off.