I am not talking about bussiness oriented forums but forums that someone has as a hobby. Btw if you don't want a competitor to install your hack then just put a copyright notice in it with a link to your forum and don't allow them to remove it Who would directly link to their competitor? And if, strangely enough they do, the advantages outweigh the disadvantages.
You know, I used to think like them and I had many arguments with opensource fanatics. And when I started making hacks I thought sometimes "hey, why release this and have dozens of other forums to have it? Why not making my forum unique with it?". It's human. But then I thought that if everybody did that then I wouldn't have all these nice hacks that are released around here, many from much better coders than I am. And also, it's nice to know you made somebody's forum a little better. It's really nice and rewarding to hear things like "awsome hack! My members will love it!".
Why not try to make the world a better place, even a little bit?