Sisko didn't commit murder. He gassed the planet, but IIRC there's no mention that the gas would be lethal, and the Maquis were able to leave the planet in any case.
Honestly, sometimes it seems like people deliberately distort the events of the episode just to serve their argument.
yeah, they said the trilithium resin he used would make the atmosphere unbreathable for humans. I'm pretty sure that means anyone there would die