Perhaps fear is the wrong word. It's more a problem of rank.
I'm an O3, and special staff to the LtCol. I hold the same rank as the company commanders, and in the battalion only two men outrank me (the XO and CO). Residency-trained docs are more likely to be O4, making them equivalent rank to the XO, and outranking the company commanders. From what I'm told, the Marines don't like this idea.
In addition, most Regimental Surgeons (at least the board-certified ones) are O4s, and there is a presumed (though not actual) medical chain of command whereby the battalion medical officers answer medically to the regimental surgeons.