Thankfully, a high speed rejected take off on a limiting runway is an event that very few pilots will experience in their career. For any pilot, captain or first officer, it will probably be the singular most critical decision he will ever make. Especially if the over-run area is also dangerous. Countless airports have lethal over-run areas.
PNF and PF political correctness aside, as a captain faced with a situation near V1 where a sudden call of "Stop" by the F/O, with no time to explain why the call was made, I would be extremely reluctant to take an irrevocable action without knowing exactly why I was stopping.
Thus, when an inexperienced first officer is given the enormous authority to decide whether the captain should stop or go - because that is why the first officer calls "Stop" in the first instance - he may have no idea how his directive to the captain will finish up. There has been countless Pprune posts over the years commenting on the new generation of extremely low hour pilots being recruited directly into the second in command seat of big jets. It is not their fault that these pilots are by default second in command with precious little experience apart from a simulator. A wrong call of "Stop" at a critical point near V1 by an apprentice type rated pilot is recipe for a disaster. Far better the first officer call the problem - not the decision.
Take it or leave it.