Nope. You have said nothing wrong, buddy!
On TE, we strictly observe 'Democracy'. So, you have the full right to voice your opinion.
And yes, this is a tech site and any technical info should be shared publically with all. You are correct & you are not denied of it!
Now the reason why a private forum is needed is that this section could be used more regularly by full members....not for spamming but for providing useful information/suggestions, etc. to the mods/admins/site managers and other full members.
Other important discussions which cant go into public could be discussed by FULL Members. This would help in generating harmony among regular members, at same time keeping those talks away from pubic members.
For example,
1. If there is some sort of competition organized on TE, and the organisers wish to know the opinion of the members about who should be given the award, then it would make more sense to ask the full members, who regularly visit the site rather than those crooks who register at the site just to view some exclusive material, post 1-2 useless messages & then disappear forever.
2. Suppose the admins need the help of some professional coder/developer, then they could ask this in the private section rather than post it publicly!
Whew! Hope that answers all your queries!