I think the left are entitled to be in a bad mood. Although it's obviously impossible to prove, my suspicion is that the Tory vote has been a bit inflated because of fears of a Lab-SNP coalition pushing people towards voting Tory. This isn't entirely unreasonable, either to suspect or even to have voted that way. The fact is that Labour collapsed in Scotland to an extent that they are lucky to have even got one seat, and to have even picked up about 25% of the vote -- tactical voting coming from people who would otherwise have been Conservative or Lib Dem voters switching to the Labour party to try, in vain, to keep the SNP out, has probably served to left the Labour vote share above 20%.
And this collapse north of the border meant that there was only a small chance of an outright Labour majority. A chance all the same -- but one that disappeared once the "stop the SNP having any influence" argument was made, repeatedly. But then, shouldn't Labour have had a bigger chance to win? After five years of Tory-dominated coalition implementing various unpopular policies, and being less than successful anyway, for that matter, Labour should have been doing well enough to be at least threatening to have a majority. That they did not is a failure of the leadership in being convincing enough.
I'm not convinced it's a triumph for democracy and I am hopeful that people from all sides of politics will appreciate how short-changed many people have been. I absolutely condemn the violent side of the protest. But I don't think it's unreasonable to feel disappointed, even angry, at how things have turned out. How you express your anger ought to be far more reasonable -- and where you direct it ought to be just as much at the Labour leadership, now gone thankfully, as at anyone else.