I can easily accept that referees will make mistakes. The pace the game is played at and the fact that they only get one look at decisions mean that it is inevitable that they will mess up.
The decision to not award us a penalty against Leicester is the perfect example. On replays it shows that it was a clear penalty. In real time I was screaming for a clear penalty, not because I was 100% sure, but because as a fan we will appeal for anything. The fact Taylor was not 100% sure justifies his decision not to give the penalty IMO. Whilst I was disappointed and annoyed, I could understand the decision. You don't want officials guessing as that is where their elements of bias will come into play.
That said, Clattenburg 100% guessed at the Sterling/handball decision. Replays show that he did not have a clear view and the fact he went ahead and gave them a penalty anyway certainly suggests so. Why he felt the need to give a penalty for an incident that he was clearly not 100% sure of, as he couldn't see it, is another matter. It could be because he is corrupt, or pro-Spurs, or anti-City, or anti-Sterling, or just wanting to be the centre of attention. In fact, it could be all of them.
One thing that is for certain, the FA cannot have referees who guess at decisions. It undermines everything that they aim to achieve.