If I had to guess it sounds like the op's statement came from the rare dankness site. They use that wording saying it weakens the strain.
Granted, I got a C- in genetics in college but I don't buy it. Why, because when they create fem seeds they use colloidal silver treatment which is an isolated event, seperate from the other male and female plants of the strain.
They're not selecting anything, they're creating. Fem seeds are created but the males and females that are left over are not effected.