Comment by j_philipp

In open areas yes, though please don't :) it's a very open world relying on each of us to do good. (Destructions of established blocks will leave dust that is traced back to you, and allows the undoing of the removal.) You can make a new area though where you can set the permission to you/ you and your friends only, meaning someone won't be able to remove a block there. Created areas with such permissions have another benefit: even your friends can enjoy them as explorers, trying to solve quest puzzles and such. I've made one such area here, for instance, an adventure game: http://manyland.com/newpolis