Why is VAR controversial?

The introduction of VAR brought a lot of controversial between football fans. Those who agree with the system declare that more correct decisions are made on the pitch and the final result is unlikely to be affected by key mistakes. Also the possibility of a competition to be damaged by a referee mistake is remote by using VAR. The video technology is able to stop bad offside decisions being made and decrease wrong penalties awarded as players will stop diving as they realise that these incidents will get looked at again.
However, fans and commentators who are against VAR in the game say that it slows the game down because of the time to wait for a decision to be made. As some decisions are too subjective VAR does not help to make sure referees judge actions right and controversy still exists. For example VAR is not able to help with penalty decisions efficiently as people often disagree about when a penalty should be given or not. Also, those against the system affirm that the instinctive joy of goal celebrations is likely to be lost due to the possibility of a video review.