Infinite downside is theoretical. The bigger problem that I learned a long time ago is that the leadership of every company is fighting against the stock going down. So if you're long a company then your interests are aligned. If you're short you really need to have conviction that it's a winning bet because everything else is fighting you. Also, it's a short term play - the short eventually needs to be unwound. So you're not just making a bet you're making one that's losing you money over time.