servers without admins, and players that impersonate others players.

[Infinity]

when I come back I dont like to see others playing saying that I insult them, tkill players, etc...

It has happened to me too, I think someone has impersonated me or telling shit to other people in my name, or they say that I do or say things that I didnt do or say.
Pox example, ALIEN asked me that if I had insulted you and he asked me that what I said to you! :> That made me think a bit in who is impersonating.. and it was a bit funny too that "I insulted you" or "I say sth bad to you" jajaja because I like your personality :D
There are people that abuse of the vote system that they vote abuse, ban evade or change tks of a player... that type of people are really annoying...

I think that AC should have a global whitelist, and ban servers that are hosted by people that cant control their servers.

Completely agree with you.
-There should be a global whitelist, that would be updated when needed
+There should be a global admin application to admin all servers (administrated by high trusted people like you, Federico, etc) and if they abuse of their admin rights (things like ban without reasons if its not indeed the ban or change map intentionally in a full server without votes of others when the vote is not like 6-1 or 5-0 pox example[some new players dont vote or dont know how to vote]) they would be blacklisted of the whole masterserver or at least not giving the admin pass anymore or during a large period of time.
+[Alternative]All servers should put in additional server info, who host it and where to contact them to apply for admin rights and it would be nice if they answer in a period of 1 week (but seeing the inactivity of a lot of players these times it would be difficult)