Where in the shirt do you put the tag?
The location could mean someone facing forwards is offside but someone in the same position looking back at his own goal is onside.
Would it have helped with the Aguero decision? Clearly his shirt was offside when compared with the shirts of Chelsea players. It was arguably the foot of Rudiger that played him onside. You can't put a chip in every inch of every piece of clothing and footwear.
The offside law needs revising. It's ridiculous that we're talking about millimetres on or offside. That's not why the law was created. We need something that punishes players who "goal hang" for want of a better phrase. Not players who start their run 0.1 seconds before the defender.
That’s the way it should be, however we clearly can’t trust referees and their assistants to make fair and unbiased decisions, so the more we can take away from them and move to a conclusive technology the better.