The 1A does not have an exception for harm.
And yet SCOTUS has carved out a number of exceptions where they felt it was clearly necessary. Disorderly conduct and noise ordinances are examples. It's not the end of the world but (very approximately) being woken up by someone shouting in the street at 2 am was deemed a larger problem than restricting your individual right to drunkenly shout at your friend in that scenario.
If that were the case than libel and slander would be legal.
Not true. Generally the law must be evaluated by the “strict scrutiny“ standard.