I think this should be one of them. You should not be able to sign away the right to work on other programming projects on your spare time.

Employment contract terms are also negotiable.

True, most of the time. But in general, for most people, the bigger the company, the less negotiable the contract terms.

That's a myth, especially for salaried people.

Companies aren't going to lose a good hire over a reasonable term change. I've heard the "this is non-negotiable", but when you get up to walk away, it becomes negotiable, as long as what you're asking for is reasonable.