Thought: In a game where a d20 is rolled for many different things besides to-hit, such as skill checks, initiative, and many other reasons (including random boredness) and crits ONLY affect to-hit rolls, then the percentage of crits is actually less than 5%.
So in a game like 3e, where iterative attacks meant to-hits are 50-75% of the rolls, then maybe it would seem like crits happen too often, but in a game with lots of die rolling (a la 5e so we hear) the crit will be rare and the need to confirm will be lessened somewhat.
Also, and in contradiction to the above, I think EVERY d20 die roll, even initiative and skill checks, should have the option to "go crit" on a 20.