Do not consider collectivists as "sincere but deluded idealists". The proposal to enslave some men for the sake of others is not an ideal; brutality is not "idealistic," no matter what its purpose. Do not ever say that the desire to "do good" by force is a good motive. Neither power-lust nor stupidity are good motives.
Most people understand that sexual lust has to do with propagating genes. Copulation in nature tends to lead to reproduction and so to more genetic copies. But in modern society, most copulations involve contraception, designed precisely to avoid reproduction. Altruism probably has origins like those of lust.