If you lack confidence that you'll be able to find at least another two job offers in a timeframe that makes you comfortable, then I agree don't quit your job.
Anyone with experience shouldn't lack that confidence though.
Your argument also assumes that I have a competing offer already when negotiating, but how did I get that competing offer? If you have a job, that solves the chicken and egg problem. If you don't, you don't have the leverage to anchor that first offer, which anchors the second, etc.
Having done both at similar skill levels, I can tell you the outcomes are much better with a job in hand.