They are afraid because they assume everyone runs significant leverage or they are just shouting hackneyed phrases: "nickels in front of a steamroller". You cannot lose more money selling options than being long/short the equivalent amount of stock.
Yes. Note the lower chart is the ATM put option which is very volatile. You could choose an OTM put to sell for less risk but less reward.
Definitely because everyone leverages up, why else use options in this context. I would note however that just because a phrase is used a lot doesn't make it somehow less accurate!
You don't have to lever up. Most non volatility based trading strategies involve some kind of leverage and thus employee the same risks as selling options.