Funny or not (I don't think I'm any different from the natives in that regard), that doesn't explain why they would find it perfectly reasonable to share the joy in public where "fun" is certainly not the aim.
Those are hardly 'facts' as much as they are anecdata. From the working class families I grew up in and around, I could assert with just as much first hand data how baseless your assertions are.
I would much rather be with a person that thinks farts are funny then one who doesn't. To each their own.