getting behind hilary clinton is an acceptance that improvements to the status quo will be slow and incremental, balanced against measures you find will distasteful, done by compromising with a deeply hostile legislature. it's accepting a repeat of obama's last few years, except hilary can't re-do gay marriage, can't re-do opening relations with cuba, can't dine on the legislative successes when democrats held house & senate, the recovering economy seems less exciting as 2008 starts to get further away, and hilary has vastly less personal charisma than obama, much less ability to frame policy arguments within a grandiose, aspirational narrative.
i think she'll be a terrific president. i'm a little scared that people are getting too excited about the ridiculous republican primaries and that maybe they could sneak sanders into the white house, and will close the door on a fantastic fighter for liberal causes and open the door to the very real prospect of republican presidency. this is a fear based argument, which is part of why it's not very exciting.