How can we be consistent in obeying international law and target “cultural sites?” Probably because there are military installations hidden underneath a number of mosques. The President is just telling the Iranian government we know about it.
While that would be illegal by the conventions on Iran’s part, the president has not said that he would strike cultural sites.
He said he would strike sites important to the culture.
And he asked “Why” he couldn’t strike cultural sites...which gets to your point.