However, to argue the converse is just as difficult. Can we really reject the hypothesis that genetics has an effect on a person's mental ability? On student success?
In China, researchers are looking at mapping the genomes of 'geniuses' to look for potential genes that impact intelligence. (http://www.wired.com/wiredscience/2013/07/genetics-of-iq/)
While, you argue from a point of pathos, that is that pursuing such genetics-based arguments of ability is dangerous and leads to dangerous situations, it is important to consider that with increasing knowledge of genetics, it is possible that we will find certain genes with impacts on knowledge and ability. I mean, even now, we know at least of genetic bases to diseases that negatively impact intelligence. Who is to say the converse won't happen? In a question of science and ethics, I would argue that it is better that we pursue, to a) not end up in lopsided world power (imagine if only China were to successfully pursue genetic bases for improving education) and b) look at potential ways of improving education across the board. If we do know a genetic bases, that may allow us to better target education. Ability is clearly myriad and manifold, and likely impossible to fully be determined by genetics. There will still be better objective measures than genetics.
To shove aside genetics effects on student success just on potential ethical ramifications might not be a very good idea.