The Lemmy developers can do good things and increase net wellbeing while being complete morons. There is nothing in Lemmy's license that says that by using their software you need to support their ideologies.
The Christian teaching of "hate the sin, love the sinner" is the best approach here. Showing support for what the lemmy devs are doing while showing how despicable are their beliefs and stating where are your differences will always work better than trying to boycott their (non-stupid-belief-related) work.