As you may already know, failing an ATLAS defense doesn't end the mission, but instead forces you to restart the defense. Furthermore, players are expected to help defend the objective(s) after the mission starts.
Whenever an ATLAS mission starts (either following a vote or after the startup timer runs out) and no one helps for a good 30 seconds, simply let the husks attack the objective(s).
The alarms, health bars, and dialogue usually spook leeches and incites them to help defend; but even if that fails, the ATLAS gets destroyed and the defense must start over.
Doing this at the start of the mission (whenever necessary) ensures you're not gonna be defending alone.
- If the leeches react, good.
- If they don't, you just saved yourself some time to find a better lobby, while the leeches will have to defend the objective(s) themselves or find another lobby.