I think when you have K-K vs. an unknown player showing a lot of preflop strength, your decision is probably roughly breakeven in terms of expectation. I usually like to just fold in these situations and find more certain times to get my money in, since poker offers many, especially against weaker players. While you might be folding the best hand occasionally and missing out on a big pot, you also avoid losing an equally large pot, which will probably happen at least 50% of the time anyways.