Ask HN: How to be supportive to people willing to take risks?

I know people who are starting a start up or on a related area, investing in stocks/companies. Usually they are very enthusiastic and optimistic about what they're doing. I'm unfortunately a lot more risk adverse and cynical about certain ideas / "opportunities" and am willing to debate and challenge beliefs, but I realize that a lot of people just want the support and echo chamber acknowledgements. I struggle with being unauthentic and genuine and wanting to share my opinions that the other person wasn't seeking.