Sure, if you're ready to 'handle' them. When you've quit your job and are embarking on this adventure, you're fragile. Depression IS common among startup founders. It's lonely at times. Those negative people can be dangerous.
But yes, at the right time, they serve to strengthen.
Except that once you start avoiding or ignoring them, it is never likely to become the "right time". Handling criticism appropriately is one of the most important skills any would be entrepreneur (or consultant or any other small business person) needs to develop.