If these are people you genuinely care about, it is worth the time investment to educate them why the idea isn't practical or useful. Keep in mind that they often do not have nearly the same insight into what it takes to really build a product or a business.
For a lot of other people (where you dont want to invest the time debating/educating them), you can offer to let them retain equity and work on it at contract rates. If you have the spare time and use for the cash, you can give them a slight discount (vs. market) and everyone wins.
(where you dont want to invest the time debating/educating them)
As a note and please don't construe this as a critique because it is valid to not want to spend time educating people, some times we are just to busy and these things can come from everywhere. But for me personally, I feel like it is my duty to the rest of you guys to educate them. I don't do it for them only, I do it for, me, them the next developer they cross paths with, educating them helps them as well as the next developer and could possible end up enriching both peoples life if they get it right.
For a lot of other people (where you dont want to invest the time debating/educating them), you can offer to let them retain equity and work on it at contract rates. If you have the spare time and use for the cash, you can give them a slight discount (vs. market) and everyone wins.