This seems to be a bit of an inadvertent red herring. We weren't discussing Starfeet's ability (or lack thereof) to prosecute a war, we were discussing the necessity of boots on the ground.
I am more discussing the fact that the fleets we see are simply far too small to accomplish such a thing, on the part of every power. I have never disputed that you need boots on the ground, I am simply saying that the idea of drafting an army, even if you could politically do so, to attempt some sort of large scale opposed invasion of a planet like Earth seems useless because no one has ever demonstrated the transport ability to move such a force.
We have recently discussed the idea of a UFP draft, and came to a general consensus that it would be at least unfeasible, and at worst the cause for huge schisms in the UFP. As to succesful invasion being impossible... hmmm. I guess you're right. Just like Savoy, just like D-Day, just like Warsaw...
D-Day is actually a good example of why an opposed landing is so difficult to acheive and it was only possibly because a huge majority of German strength was deployed against the Soviets. There were nearly 160 German Divisions in the Soviet Union against just about 60 in France. Simply put if that landing was all the Germans had to worry about no amount of planning or effort would have made it possible.
Again, I am not saying you can't invade a homeworld type planet. I am saying that you will need likely tens of thousands of ships to carry the troops necessary to do the job. Hell, D-Day needed nearly 7,000 ships and they were crossing a narrow body of water. The Amphibious Fleet for the invasion of Kyushu had over 1,200 major ampibious ships, plus thousands of landing craft.
Of course nobody wanted any part of it - it would have been awfully bloody. But the U.S. was certainly ready to do it, and had more than reasonable hopes for success.Saying that nobody wanted any part of it is both obvious and irrelevant. Nobody would ever want any part of any type siege or invasion, but almost everybody recognizes the need for such at times.
The point being that after the course of a long war the US, which was going into WWII a pretty pacifistic nation itself compared to the other major powers, was looking for any alternative to spending a ton of their own lives to enforce an end to things. They were willing to starve, fire bomb and eventually use the most powerful weapon anyone on Earth had ever invented in an effort not to have to do it. Serious consideration was given to using chemical weapons as well.
I have no problem stating there is a huge value in Marine type units. The ability to invade and take a particular planet is something everyone needs to have and there are plenty of smallish colonies and resource type planets that it would make sense to take from your enemy and hold.
I just don't see the ship building capacity to pull it off against the most populated worlds unless they give up on their own accord. We would need to see much larger fleets to really imagine that this was possible IMHO.