Fair points. We can get some distance with solar, wind, tidal, geothermal, etc.  But, ultimately, we're not going to be able to maintain anything resembling the lifestyle to which U.S. residents have become accustomed unless population is greatly reduced.  There are many pieces to the puzzle, and most of the folks involved in the divest movement are aware of that, even if they don't try to address every piece in every action or communication.  (Most audiences have a short attention span.) 

 The piece that they are addressing in this instance is a critical one, since every year that we pursue status quo energy policy is a year in which we dig ourselves into a deeper hole.  (A screwed up climate will make all the other needed transitions even more expensive and uncomfortable.)  Neither the politicians nor the marketplace are going to start seriously investing in substitute technology production unless and until we start to be forcibly weaned from oil.