Heck, I've got two cents, so here goes:

Blowin' in the Wind--khandu and Spaw (catspaw49) explained this pretty well.

Ohio--Joe Offer's link to a previous discussion and Metchosin's links give more than enough info on this.

Where Have All the Flowers Gone--Wavestar and Spaw covered this; I also see it pointing out/bemoaning inability to learn from the past.

For What It's Worth--Discussed quite a bit in this thread. This song stands out in my mind for its balance. Most protest songs or songs about the protests and protesters seem to take it as given that "the establishment" is mean, cold-hearted, and wrong, while the protesters are all warmth and light and the only ones who make sense. "For What It's Worth" mentions the foibles of all involved, and is refreshing in its evenhandedness.

War--The meaning behind this is that war is not a good thing. Which is exactly what the song says, ad nauseum. In other words, the meaning's not "behind" the song, it's right there in front of you, hopelessly transparent and obvious. Is this a trick question, hinting that there's a "hidden meaning" in this song?

People Got to be Free--Two trick questions out of six? I wouldn't call this a protest song. It's musical pablum, with a message reminiscent of the average six year old's grasp of complex issues: "Let's all be nice to each other." It represents the flower child/love dimension of 60's/70's culture, but I sure don't see any protest in it.

Who, me, opinionated? Nah. Seriously, I hope this helps some.