Oh, dear Lord.

If you have to ask: USE A BRAKE!

If there's any doubt in your ability to stop safely: USE A BRAKE!

Just taking off your brake to 'get used to riding brakeless' is a terrible idea. Try having a brake, but avoid using it as much as possible, to get used to riding brakeless. Once you've put a ton of hours in on your bike without having to touch your brake, then think about taking it off.

But still, as fast as you can be without a brake, is still slower then you would be with a brake. If you want it for the 'zen' or whatever bull**** hipsters tell themselves, go for it, I could care less what you do with your bike.