I don't think everyone should be able to get access to "sneak attack". Everyone should be able to score a critical hit on vital areas, sure, but if you're going to make a distinction in the overall fighting style at the class level there's a distinction to be made between the tank fighter and the finesse fighter -- and using stealth and swiftness to your advantage definitely falls into the finesse side of things.

Arguing that such a basic question of fighting style not be class-oriented is more of an argument not to have classes at all -- which is fine, if that's what you want to argue, but it's pretty fundamental to the nature of classes to begin with.