Well, you can follow the same strategy against all players, or you can adjust your strategy against different players depending on their aggression and playing styles.
And no, limping does NOT mean always limping AA and KK.
Listen, if you have early position with lets say 55 and you have mostly calling station types behind you, do you really think you are gonna kick ass by playing 55 aggressively? You are gonna get like 3 callers and how often are you gonna flop a set? And how often are all 3 guys gonna completely whiff the flop? if these guys are gonna call ya down if they have anything, then you are just kidding yourself if you think you are gonna bully them.
Or, maybe, you can see the flop for cheap and if you do flop a set, you can value bet these stations accordingly.
Yes, in general limping is a bad idea against competent and tough opponents, but you have to know there's no "always" in poker. You have to play the opponent(s) at the table.