Without shorting, stocks tend to become more overvalued, since people can only sell stocks they've already bought. With naked shorting, people can bet on return to mean on the downside, thus depressing long-trends and allowing improvements on price discovery mechanisms in the market. General consensus seems to be it's a means to avoid too large bubbles as you provide tools to "invest"/bet to the downside as well.
Good question. We can't all know everything, and I know I know very little. This is the kind of stuff you read once, and then just remember it. Might be inaccurate, though sounds logical and markets generally seem more mean-reverting now than decades before.
Think of it as removing some of the pyramiding effects of stock-manias. However, if the market tanks too much, regulators might freeze shorts or start seizing assets. I don't think you get infinite money if stock goes to 0 either. It'll probably hurt too.. So shorting is more short-term, risikier and faster than long. Due to liquidity-reasons, most brokers probably offer shorts naked when offered upfront.
Btw, any logic can be made illogical.