Wearing a t-shirt purchased at that mall does not belong in the same category as drunkenness, public disturbance, or vulgarity. I agree that the students banned for wearing anti-abortion shirts to school is ridiculous, but lets not be hypocritical here. Freedom of speech means tolerating messages you may disagree with.
No, it does not mean that at all. It means that government shall not make a law limiting the free exercise of speech. Read the First Amendment! Tolerance is not mentioned.
If you decide to spout off on my front lawn, and I tell you to leave, you better go, or you can be arrested and convicted of trespass....and free speech will not matter a whit. Malls are "private property" in most states. Failure to leave when asked is misdemeanor trespass. Your shirt won't save you from being ejected or arrested.