And if you're not on a PPS pool trying to sabotage it, what is the reason one would want to do this? Yes it does withhold blocks, but virtually every pool does not use pps and you stand to lose btc by performing it on them.
You still get paid when someone else in the pool finds a block, basically you are sabotaging the pool for your benefit only. The reward is certainly lower and it hurts everyone mining in that pool; but the side effect is that your hashrate will NOT increase the difficulty as it's not contributing to the actual block discovery rate. A party with a large hashrate can thus over time potentially realize more income by stealing from pools using this method, as the hashes he is contributing don't increase difficulty.
Possible Solution
When a pool finds a block, transmit the successful nonce to other miners in the pool. The miners that don't respond with a valid block are cheating you...and thus their account should be locked from future payouts.