On contrary to that. Ive found that a great marine player will verbally converse with the commander, support or contest the strategy, but ultimately strive to help the team win. So in the case if a comm is making a mistake, he will correct the comm. In any situation he will suggest what to do first, as he is in the best situation to do so. For example, the minimap basically shows everything that the commander can see. However, the commander always has to keep an eye on the main viewing area of the map, not the smaller minimap in his left bottom corner. The marine on the otherhand always has time to check his minimap, and whats better, is that he is there in person, so he knows (given hes already a good player, ie good shot, and good players kills in communication, hear, good common sense, etc) what should be done. Ive seen a lot of commanders drop resource towers without asking if its safe, and then having to watch a skulk kill the marine, and losing the tower.
The marine alone knows whether he can complete an objective or not. So I rather have my marines (when I comm), not only follow orders, but tell me whats going on around the map. I could go on and on about how a marine should play NS, (I wrote a 21 page faq on what 1 marine should know and how he should play), but you probably get my point.
Sometimes you need to prod the marines a little, ask them a little more, goad them to not get ammo, but patience is key, and it build relationship between marines and you as a comm.