People are sickened / embarrassed / ashamed of that, and a fiver to a crowd-funding page is the one means they have to express that, in the hope of making the kid's life easier.
It also allows us to demonstrate very visibly that there are many who totally and absolutely oppose racism. In the current toxic and hostile British environment this message needs to get out there, it needs to be shown that those with immigrant back grounds do have friends and supporters.