1. Lead with your bias. 2. Avoid cheap shots. 3. Be your own biggest critic. 4. You can still talk shit about software, just not your competitors‘ software. 5. Be generous with your expertise.
The question though, is why does money ruin everything? The naive questions of an open source zealot to a proprietary software salesperson are one thing, but since we all need money to live, why does money being part of the equation (eg if someone was getting paid to post here) ruin things? Would a "donate to open source" button be more successful if the donate text is "buy me a coffee", "buy me a beer", or "upgrade my beer from Coors light"?
https://xkcd.com/2347/ was and is true, and if we don't figure out a way to change that, I don't really see a future for open source.