1. The Conservative Government Is Legitimate
David Cameron's Conservative party won 331 seats out of 650, thus getting 51% of the seats, whilst this is a very narrow margin, never the less it is still a clear majority which was freely and fairly voted for by the public.
No matter how much the result has frustrated many, they must realise this is a democracy, where sometimes we agree with the majority, sometimes we don't. Think of this what you will, but a society is much fairer when a majority rules over a minority than vice versa.
2. The Electoral System Actually Favours Labour
'In 2005, Labour won a comfortable majority of 66 seats with a lead of just three, but in 2010, the Conservatives failed to win one at all with a lead of seven.'
From the New Statesman article: 'Labour's electoral advantage isn't mainly due to the boundaries'. (Published January 2015)
'The current system is biased in a technical sense, not in a pejorative sense. It's biased in a technical sense because of a variety of factors: first, the constituencies are smaller, Labour gets more MPs for the same vote share than the Tories get. It's historical in the sense that Tory areas – the wealthy shires - have tended to have faster growing populations over longer periods, so they inevitably expand. It's not a deliberate bias.
The second factor is low turn out. In traditionally Labour areas, often inner-city, poorer communities, the party actually benefits from lower turnout.'
From the Guardian article 'Reality check: is the electoral system biased in favour of Labour?'
3. The Voting System Is Unfair To Smaller Parties - But The Chance To Change It Was Wasted
The First-past-the-post voting system has been a staple in British Politics for years, however over the past few years it's been seen as more a hindrance in democracy due the emergence of smaller parties. The system itself favours the larger parties due to the idea you can only win seats by having areas of concentrated support - which smaller parties often lack. Because of this UKIPs roughly 4 million votes this year only amounted to 1 parliamentary seat.
However many people fail to remember that Nick Clegg early on in the last government and proposed a change to the voting system, his plan - The Alternative Vote. Whilst more complex than the first-past-the-post system it was fairer all round. In 2011 there was a referendum for the AV that had a very low turnout - 42.2% resulting in an overwhelming majority (67.9%) voting against it. So those angry at the current system must realise the majority of people wanted to keep our current voting system.