Or are you saying that forgoing salary is always a bad idea? If you are, how else are we supposed to start a product company? It seems like it's a worse idea to take investment without having done some minimal homework and prototyping to prove out the market, which usually requires at least building something you can show to customers. It's a very bad idea from a legal standpoint to do that work while you're still employed by somebody else. Consulting -> product conversions can work, but it's often really hard to make time for product development while consulting.
From my own perspective - I started a "founders don't take salary" company when I was 2 years out of college. It failed miserably, predictably - it was a terrible idea to begin with, and I folded it up once I realized I was in over my head. But I think starting it was one of the best decisions I made in my lifetime, because the skills and perspective I gained from it got me a job that paid enough that I made back that year after about a year of employment. I'm now in a position where I have a bunch saved up, and I'm trying to weigh my options rationally. I'd like to avoid making stupid mistakes, but I'm also mindful of how the #1 regret of most elderly people, on their deathbeds, is that they wish they'd taken more risks.