What point is there to it?

If he/she feels the need that he/she shouldn't be in the community. Than he/she has all rights to ban that user without a notice/reason to the user

He/she don't have to say, "I ban his/her username because it's going to cause a problem."

If an admin ban a user without a reason, than it's call ABUSE of power. Because he/she isn't giving a valid reason for that users to be banned.

You seem to be flip-flopping between no reason needs to given and yes, a reason should be given.

Let's be clear. No reason has to be given for banning. BUT there is always a reason for banning.

If someone join my community and I just want to ban him. Guess what, I'll do it.

Do I need to give a reason? No I don't need to give a reason. There might be a reason behind it (is there, maybe not?).

EvilAkuma, I uderstand that English is not your 1st language, but there is no need to keep stating the obvious over and over.

There is always a reason for everything someone does. There are no exceptions.

There is "always," but in some cases, there isn't.

LOL! Humans always do thing based on a reason. We are what is known as "purposefully beings".

Give my just one example where there wouldn't be a reason.

Someone decide to join my community and I just ban that user.

Don't try to ask why because it'll just go in circle.