>Given your first line, this sounds like a bad faith suggestion. Why should I walk away from something promising vs helping our team become more productive?
You presented two options: stay and try to fire the other guy, or leave. I presented a reason why you shouldn't stay, and suggested you leave. Not sure what about that appears to you as bad faith.
>And given the context of the person in question, who was fired from the last startup for lack of productivity, I don't think this will do much to my reputation.
But you're not going to control the narrative; your fired coworker will - unless you're willing to go door to door and publicize the fact that you got that person fired, which is a terrible idea.
>It's out of wanting to work with excellent people and build an excellent product.
You generally don't get to do that by punishing people who recommend you for jobs that you find fulfilling.
I've always found that the most talented people in a room tend to gravitate towards one another; so too do the most toxic. If you keep doing toxic things, don't be surprised when you find yourself surrounded with people just like yourself.