I don't agree with booing either. I think it's wrong but at the same time, I have an issue with people who seem to equate the BLM movement and the whole kneeling thing to racism movement. The situation is much more complicated than what it appears.
I also find this whole kneeling this very half-arsed attempt by the British to try to virtue-signal. If England truly believe there is a racism issue, why can't they kneel during the English anthem instead of kneeling before kickoff? The USWNT knelt during the anthem for a whole year, and it takes incredible balls to do it. Megan Rapinoe knelt during the anthem before the whole George Floyd incident even took place.
How can people kneel to God if he isn't real? Well that's your faith but you can't make that decision for everybody. Everybody has their relationship with their faith in different ways.