Adults have a small chance of acquiring those traits too. Due to selection effects adults that don't have traits have a much lower probability than a fresh new baby of turning out this way.

As well as, of course, as having far less malleable minds that have yet to crystallize the habits their upbringing gives them.

Are you ok with babies with very low probabilities of getting such traits being killed?

Far less averse, particularly in an environment where negative externalities cannot be easily prevented. Mind you I would still oppose legalization of killing people (whether babies or adults) just because they are Jerks. Not because of the value of the Jerks themselves (which is offset by their effects on others) but because it isn't just Jerks that would be killed. I don't want other people to have the right to choose who lives and who dies and I'm willing to waive that right myself by way of cooperation in order to see it happen.