Only true in a very narrow sense. I always find it awkward to hear Marines called soldiers, but in only a slightly broader sense of the word, they are.
Besides, the modern Marine Corps functions as light assault infantry. They don't stand in the halyards and fire muskets at the capt'n on the deck of the enemy ship.
Me, too. That's why I posted what I did. Ain't trying to be snotty or nuthin. The average person may not know that. Since I was both a Marine in the USMC and a soldier in the U.S. Army, I have a little bit of knowledge on the subject. Marines shouldn't be called soldiers any more than sailors or airmen are, no matter what their function was.