No, some countries use referendums for lots of things, like Switzerland. Including quite small things like whether or not to build new tunnels. Simple majority

No, some countries use referendums for lots of things, like Switzerland. Including quite small things like whether or not to build new tunnels. Simple majority has the advantage that it's fair. If you're going to start claiming that decisions that will "profoundly impact everyone" need higher than majority you're just going down the road to totalitarianism. Anyone can claim a decision they think they're on the losing side of is too important to leave to majority decision making. Then it's just about ramping up the threshold until you win.