The only thing that would hamper modern soldiers is that from everything I have read medieval knights weren't possessed with any qualms about killing; life in general was much more violent than we experience now.
For more reading about this mindset, acoup.blog [0] has an excellent review of Bertrand de Born's work. What struck me is just how casual violence is treated, and that war is a treated as the expected normal condition. The peasantry definitely did not hold these views, but given that the nobility had a vast armament advantage and copious experience in killing I doubt many modern soldiers would be quite so callous. The only modern exception I can think of is child soldiers; but they have been subjected to abuse specifically to train them to be able to commit horrific acts. Maybe I am wrong, but I don't think most soldiers in modern militaries would easily be able to slaughter their countrymen with quite the same abandon. This is speculation, but I suspect that the nobles were able to do this because they viewed the peasantry as semi-subhuman; see the American antebellum south for the types of atrocities that that mindset enables.
[0] https://acoup.blog/2020/04/16/collections-a-trip-through-ber...