In other words, short sells are tools to use against failing companies, not against markets you think can't deliver real value. Markets are much bigger than companies and can make short work of your maintenance margin even if they're going to crash in the end.

If you want to make a long term bet against a market, the best idea is to figure out who benefits when that market crashes and go long on them.

Shorts are also useful when you have private information the market doesn't have, yet. (As opposed to bad news the market already knows but chooses to ignore.)

Ie: dig up dirt on a company, short their stock, publish bad news, close out your short position.

Who wants to go long a company (ie invest in equity), should welcome the ability of others to short: it ensures you can buy for a fair price and that there's a smaller likelihood of skeletons hidden in their basement.