Halo is no wimp- he survived for months, on his own, on post-holocaust Caprica. He had given up his seat on an evacuation shutte so civilians could flee. His refusal to commit genocide is an important point in the series- it's turning out that the cycle of near-genocide has been going on for thousands of years. Halo took the moral stand that the cycle has to end somewhere.
Never mind the fact that the Cylons tried to do exactly that to humans and were almost successful and never mind that the Cylons are freaking machines.
Which was kind of the point of the episode. Does any species have the right to commit genocide on another sentient species?