That is probably right, for many of them. When I was in college during the late 60's, I thought the same of the anti war protestors then. I figured the real motivation was that the whole thing gave some of the kids a chance to feel important and be noticed. I didn't realize at the time, though, that many of the main organizers were actual commies, just as they are now. Then, as now, it was not widely reported by the media.
'Course I was somewhat sympathetic at the time, didn't want to really go to Viet Nam, considered myself a liberal, was an art student, etc. I knew enough, though, to understand how evil socialism was, just didn't know enough to know that "liberals" had become socialists.