I'm not sure that "conspiracy" is the right word, but there is no doubt that external forces and match situations influence decisions.
This is typified by the fact that week-in, week out, fouls given outside the box would not be given if they were inside. I think it's also often the case that a red-card is more likely to be shown later in the game than earlier on, for the same offence.
It's easy for a ref to send someone off when his team is 3-0 down with five minutes to go, but to send off a star player that people have paid money to see when it's 0-0 and five minutes in... well that's a different matter.
Easier to give a penalty to the home team too, refs are human and a baying crowd of 50,000 rags would influence anyone.
As to today's decision, I can imagine that the ref might have missed it, easy to miss a fairly small push when you are behind the players (which I assume he was), but the linesman must surely have seen what happened and is probably to blame here.
On the plus side I thought we played well, really well, but I'd love to Serge banging in one or two more and I reckon Sterling needs a run of goals to get the balls to shoot again.
We aren't going to catch Chelsea, but on today's form I think top four is achievable.