Why not? Lots of things are illegal regardless of what people put in contracts. If I contract you to kill me, you'd still go to jail for murder. Lots of things are illegal to sell unless they meet quality standards, regardless of if consumers know about it being sub-standard or not or agree to it.
Society has decided it just doesn't want to have to deal with that kind of crap and it's annoying consequences for everybody else. I'm against the general principle of hundreds page EUAL fine print being enforceable. If the industry wants that sort of thing, they should agree some set standard contracts vetted by the government that meet specified standards of service and consumer rights. We shouldn't have to deal with obscure and impenetrable special exceptions to everything all the time.
For the initial sale of it, yes. But not after that. See below.
> Don't you have a legal right to enter into a contract with your shoppers (i.e. You agree to purchase consumable products for consumption only and not resell them)?
You couold put that on your package, but legally, I don't think it would pass muster as a contract. Even if you got each customer to sign a form agreeing to such a contract, I'm not sure it would stand up in court, because statutes have limited what rights a customer can sign away even in a written contract. Which might not make sense, but lots of things in the law don't make sense. :-)
(The usual disclaimer that IANAL applies.)