First of all, you can still place TNT, as much as you like, build a house out of it for all I care.

Second of all, you cannot entirely ban TNT as an item, there are always ways around. (= inventory hacks)

and finally, TNT is being prevented from detonation, but the intent to detonate it alone shows me that someone just doesn't get it if I repeat 30000x not to use TNT. And if one can't comprehend that, or doesn't want to. It shows me that he/she is probably not a team player or a rule-follower, and I don't want that kind of person on my server.