[Double Down]

I reraise with kk preflop for a couple reasons.

1. I like to know where I'm at and want to get it all in there preflop. I have laid down kings a few times preflop when I KNEW that the guy had aces, and I could not have done this unless I reopened the action preflop. Let's say you call and the flop comes with jack or queen high. You have no idea if you're way ahead or behind. Let's say the flop comes with an ace. If you are ahead (and he has jacks, queens, etc.) then it will be hard to get a lot more money in there. And that's if he doesn't bet you off of it first.
If you isolate, it's a lot easier to call a large bet on a rag flop if it's just you and him, and not if there are 4 or 5 players. Overall, there are too many sticky situations that you can get into on the flop with kings and imo, the time to get money in with kings is preflop.

2. Someone else touched upon this. If there is no strength shown preflop but rather after the flop, then you probably have a couple of hands going up against each other that are at least 2 pair. If you just call your kings and then start betting big after the flop, your opponents will probably be worried about you having 2 pair. This is why I also raise good hands in the blinds, because if I didn't and my action is big on the flop then people have me pegged as flopping 2 pair or better, and if they won't pay me off with a worse hand than a big pocket pair, then they definitely won't want to get into it with me if they think that I have better than that.

It's okay to let your strength be known by raising because
a)You will protect your hand
b)You are getting value for it
c)The way your opponents react to it will define THEIR hands.

And even if you reraise, there will be enough mediocre players hanging on to AQ, AJ, KQ, QQ, and other pocket pairs to make it worth it.