“my question is (partly) if someone gets pleasure from burning things (ie a pyromaniac) allowed to destroy an issur hanaah by burning it?”
Now this is starting to get silly. You can’t derive benefit from the burning substance (eg. cook a barbecue on it). If the pyromaniac gets pleasure from it, he’s just enjoying the mitzvah. Just because he would also enjoy burning newpapers wouldn’t make any difference.
I’m not sure if it’s more linguistically accurate to translate hanaah as “pleasure,” but within context I think the translation of “deriving benefit” usually gets the point across more accurately and deters these kinds of questions.