I think you're a bit confused. The only hand you don't want to be called by is AA; you're so far ahead of any other hand including any ace that your absolute ideal should be getting it in pre-flop against Ax.

The thing is, your argument here makes sense - isolation is a very important concept and is one of the biggest reasons why we raise. But EV is too central a concept to allow your comment to go unchallenged.

If you get called by Ax and an ace appears on the flop, then bad luck, but KK is foldable. It's second pair with only 2 outs. Standard move is to make a pot size bet and, if you get called (on all but the dirtiest flops), slow right down. Just because a hand is the near-nuts pre-flop, it's only ever one pair.

So yes, you are correct to raise to isolate with KK, but you should be just as happy for A9 to call you as 89. Which is more likely to stack off to you on a 249 flop? Or AQ on a Q-high flop? With the Ax hands where the lower card hits, the fact that they have top kicker makes fish feel invulnerable and you'll make that much more money out of them.