by default it's no holds barred pvp, like garry's mod RP without the rules. most servers that don't completely rework the game use strict land ownership so you can at least keep people out. streamer-only servers are very different from actual vanilla minecraft, which almost no one plays due to the chaos, violence, destruction, etc.
it's basically rust but without any form of locks or armor plating. someone will eventually come along with a wither and delete your base, at which point you "lose." it's not really a multiplayer game and never has been, if you're not with a handful of personal friends it's one of the most unpleasant online experiences you can have.
the problem is... even with plugins, 90% of the time it's still regarded as an explicitly competitive pvp game. and it's a meat grinder for new players who don't know how to fight.