I can agree with a lot of this, I suppose it depends on the position of the player and situation in a match. For example CB is very hard to blood young players on because a mistake can lead to conceding a goal which could lower confidence. However, a winger/forward is less likely to have an impact on a defeat because in theory if they lost the ball in the attacking third, there should be enough cover in place. The same as game situation, if it is tight then it is a risk bringing on the youngster as it could affect the result. But if the result is seemingly already decided (winning/losing by a comfortable margin, with a short time frame left) then in my eyes putting the young player on for a few minutes is a better option than a tried and tested player.