Clinton too extreme, rejects First Amendment's core rights: political speech, democratic participation
The most important reason not to vote for Clinton is her hostility to the First Amendment -- several positions that are neither extreme liberalism nor extreme conservatism, as we have usually understood those terms, but are all the more extreme for being totally unplugged from liberal or conservative traditions.
As for everything else, a lot of her imperfections are things we've had before in presidents; obviously she's not the first big-gov't economic lefty, nor the first to tactically hatemonger and demonize her fellow-citizens who disagree with her on that. I don't remember how Wilson, FDR, Truman, Johnson & Nixon did that, but Bill & Obama at least sounded like they still valued all Americans and beckoned the misguided back to the fold, while the media happily did the dirtier work for them. They usually singled out legislators & advocacy group leaders as the evil extremists. HRC, on the other hand, pretty clearly indicates that if you're opposing or obstructing anything, then none of your rights or interests matter, you don't matter, and you should just get swept off the chessboard.
But that's not what disqualifies her: it's the hostility to the First Amendment and her vow to amend it. First there's all the attacks on people's right to morally disapprove of, and choose not to participate in, certain actions that their religion has disapproved of for millennia. That's already been going on in the Obama administration and at every level of government. And the campaign finance reform, extending the notion not just to giving money to officeholders and candidates, but against any political speech against candidates, or even about referenda, if the speech costs money or involves banding together in groups, e.g. Citizens United. Which means any speech that's significant & effective enough to make any difference.
The First Amendment is what makes us America. We'll always have differences about where to draw lines in the gray areas around it, but somehow liberalism has turned around 180 degrees from when I was a proudly liberal Democrat in the 70s and 80s, and it now wants to cut out the heart of the 1st Amendment as it has always been understood from the founding up through the present: political speech and freedom of conscience.