The reason that the Neutral role sits quietly and doesn't draw attention to itself is because the best way to survive is to have no enemies. Once you pick a side, bam, the other side is your enemy. Admittedly, if you're skilled enough, you can play both sides, but that's difficult. Now, let's say you add a kill. The Neutral is now a potential asset, sure, but he's also a threat. To both sides. Add on the fact that he MUST use his power, and he's a loose cannon. Probability-wise, it's likely to help wolves more than town, so town will be out to lynch him. But it's also a kill that can kill wolves, so wolves are perfectly fine with finding and killing him. Simply put, a kill is more of a threat than an asset.