I started as a scuba diver and a mathematician. I co-founded a company, OFEK, in Japan and sold it to my partner, to become a derivative trader. After a few years, I founded a second company, SNI, and sold it. I became a lecturer at a university in Australia, climbed a few mountains, rode motorcycles around Asia, and did more scuba diving. Then I joined a few multi-national FinTec companies (Misys, WSS, Askari) and developed their businesses in Asia .Then started another company, and failed. In recent years I combined helping companies from the inside (head of division, head of region, CEO) and helping startups as an adviser, board member and an investor. This year I picked up skydiving, skiing and flying. I hope to get better at all of them this year, and brush up on my Japanese skills.
Actually, the reason I think one should not work for no cash is a different one. Working for equity only is the equivalent of investment in the startup, and there is nothing wrong with it in principle, if you can afford it. For years I worked for equity only, and accumulated a nice investment portfolio (as a business consultant rather than a developer - but the principle still holds). The main issue I have encountered was that many startups do not feel the pain when giving an equity, and often will not prioritize their work with you. That means that in addition for not getting paid cash, you also waste a lot of time.
My model at the moment is to charge 30-50% cash and the rest in equity. That help me build my startup portfolio, normally not to expensive, cash-wise, for the startup,and still they feel it enough to want to help me with my work as quickly as possible.
What I said here is exactly what I tell the startups. And if all they are willing to give is equity, I tell them I see nothing wrong with that, but that I am not the right person for them.