The danger is that adjusting the margins isn't going to remove speculators. It's trying to solve the symptom rather than the problem. I don't think the underlying upward pressure on crude is speculation based anyway....if you look at the crash in silver and the lesser crashes in gold and crude, you'll find that it may have been marginal reserve requirements that sparked it, but it was the real broad dollar index's rebound that eased commodity prices.
As we see, we're climbing again, not because of speculation, but because our dollar is worthless.
If you REALLY want to get speculators out of oil, the best solution is to remove the speculation by pumping more supply into the market.....you'd find the bullish speculators run for the hills very quickly.