Is there anything positive to this “one nation can veto everything” rule? It feels like this is really blocking a lot of progress in the EU where some of the right-spectrum nations can simply block anything or bargain from.
Why do we have this rule and is it hard to get rid of it?
Many people, and nations, would be hesitant to join a union where you can be coerced to tolerate neighbors you otherwise wouldn't. Hence the idea of consensus.
You cannot really get to anything you can call democratic voting, it would be so random and indirect that it would basically become meaningless. So states still need a hard veto for themselves and the direction the EU will develop in.
It's that exact trend that led to Brexit in the first place - your comment shows why it's problematic perfectly. EU supporters see it as a way to force left wing politics onto populations that otherwise would reject it.