Why?

If the males survive then they can pair with normal females and use up their resources. Say I have 2 boys, and 2 girls, all die that's 4 people who won't have babies. But say the boys live and marry 2 girls. Now we have 2 dead, and 4 who can't reproduce, for 6 total taken out of the healthy reproducing gene pool. Every male with the gene who finds a life partner also takes a otherwise healthy fertile female out of the gene pool as well.