Yes, those people in Florida are entitled to burn the Koran. It is not a crime. It’s important to realize that in the US they are free to express themselves in that fashion.
No, they are not destroying knowledge. Other copies exist.
Yes, it is an infantile act.
Yes, it is likely to cause harm to happen to people who were not involved.
Yes, Hilary Clinton is perfectly entitled to criticise the reverend and ask him not to do it.
I hope they are not stupid and childish enough to carry out this act, but they are free to do so, and it matters that they can. It also matters that the people who are waiting to be offended by it realize that they can do it and no one can stop them except by persuading them not to.
There are deeper, much more complex matters involved, but these questions need to be clearly understood before the rest can be seriously considered.