the entire concept of 'private mods' is ridiculous. if you make a mod, you better well expect it to be used, private or not.
I'm assuming that you mean a mod which is released to a hypothetically closed group, not a mod which is hosted on a single server.
If my assumption is correct: Yes, I agree in full. You can't keep a mod within a closed group, and shouldn't expect or try to.
If my assumption is incorrect: Good to know, I'll just release all of my
unfinished and unstable mods for everyone to crash their servers with.