Can you have a dog without a permit to walking him in the park?
Precisely. If you don't want to walk your dog in the park, you don't have any reason to want to register your dog.
In the US, you "get" a trademark by using a distinctive mark on your goods/services. If you want to enforce that mark, you will have to prove in court that you've been using it, it is valid and distinctive, that you own it, that it is enforceable in the jurisdiction where you are suing, and a few other things. The burden will be on you to prove those things in order to enforce your mark.
If you have a trademark, and you then REGISTER your trademark, then you (a) automatically have the right to sue on that mark in federal court instead of state court, (b) you walk in with the presumption that it is valid and distinctive, and that you own it, (c) your right to enforce automatically extends to the entire US and is not geographically limited to your trading area, and a raft of other enhanced rights. In other words, registration shifts the burden of proof on those things to the alleged infringer. Instead of having to prove you DO have a valid trademark in the case of an unregistered mark, your registration says you have one, and the other guy has to prove you DON'T.
But registration of your mark in the US does not "get you a trademark". It confers certain enhanced procedural and legal rights in the mark you already had.
A similar situation is true with copyrights. If you write a work of orginal authorship, paint a painting, compose and record a song, etc., you HAVE a copyright in your work. Automatically. That will give you the right to stop others from copying. If you want to sue for monetary damages in federal court, you will have to register your copyright. But registration is not what gets you a copyright. Registration merely provides you with certain conveniences and shifts the burden of proof as to whether you own one.
