The World Cup is luring and we are remembering the Euro 96, when Bulgaria was denied a clear goal, when controversial offside refereeing might have also prevented the Netherlands from advancing. We remember 1966, when a situation decided on the World Championchip, that 30 years later is still not doubtfree analysed. If referees were bad in general, at least one in the world might have come up in all the time who obviously is better than the others, who sees everything right, who makes no mistakes. But this is not the case. You find even the best and most accepted referees make totally wrong decisions, even have a complete horrible match from time to time.
Some cases are clear.
But most cases can be discussed. A goal keeper going for the ball and does not get it. The attacker, maybe not finally trying to jump over him, takes the foul and gets the penalty. Many of the controversial situations are in a grey area that has to be interpreted and can be either interpretated this or that way. This is a property of the game.