I have used a similar argument when discussing how homosexuals are actually safer under strict Christian rules then if they were left to the rules or beliefs of Darwinistic athiests.

While Christians will declare that homosexuality is a sin and will work to keep it from becoming mainstream or acceptable as marriage, the opposite of that has a very ugly past. Christians are not called on to eliminate or kill people because they are homosexuals. However, while atheists will not view or see homosexuality as a sin or evil, they will and do eventually see homosexuals as a weaker “species” and that does lead to the “elimination” option.

Whether or not Darwin himself proclaimed specifically “survival of the fittest”, his dogma/doctrine/teachings lead to that way of thinking. If something is not making your species stronger or better then it can and should be eliminated. While most atheists are probably not for forced elimination, their dogma of life without a final judgement with God makes that option quite open.

It only takes a few powerful atheists in the right spots to force their “elimination” effort (if all Christians are neutralized or removed from the scene).