American here - we have a lot of family friends with kids who are very into “soccer” and are interested in seeing games abroad. I’m on the East Coast so it’s a shorter trip to London and generally families interested in football here are more affluent. Because the London Stadium is big, I know a lot of people end up there when they just want to see a game - they don’t necessarily have a specific team they support. Friends went there last year and ended up sitting next to long time Hammers who told them all kind of stories and taught them the songs and they came back to the US as fans for life. Not all tourists are terrible! And many I know are smart enough to know to behave and dress appropriately whatever side they sit with, even if they usually support another team (obviously support is more fluid here in the states).