Actually froggie. hitting is assur becasue it is a lav in the Torah of Baal Tosif and as codified by the Rambam. If not for the pasuk forbidding it it would be allowed. (Of course there is also Veahavta lereicha etc…) But there is in fact a passuk in the torah and halacha in shua forbidding hitting.
Things arent assur becasue they seem assur they are assur if the Torah/Chazal/Poskim tell us it is assur. if you dont know if it is assur there is noting wrong with asking whether it is of more knowledgable posters or of your Rav.