With lasers that powerful, it's not just about aircraft. If you pointed it at people intentionally you could blind them, which makes it a weapon. There's tons

With lasers that powerful, it's not just about aircraft. If you pointed it at people intentionally you could blind them, which makes it a weapon. There's tons of stuff that has legitimate scientific uses that needs to be licenced for lots of reasons. For example, you need a licence to have iodine with concentrations above 2.2%.