I bought Silent Running off of Ebay a few days ago, and watched it on Sunday. The protagonist wasn't a laid-back hippy, he was a militant environmentalist. Of course he was wrong to murder those people. We don't know the political system he was living under, but if it was a democracy, then he should have taken part in the democratic process to try and achieve his aim.
All good films have a happy ending. So did Silent Running have a happy ending? Well I suppose there was a faint message of hope in that the forest sailed off into the sunset.