Calling it hate is an exaggeration , people are entitled to their opinion and informing other people by criticizing snap.
Another advantage not mentioned is that snap is a product of canonical (a for profit company talking about an IPO for years), flathub is managed by the gnome foundation (a US registered non profit, which should provide some legal protection).
Fundraising is skill, and it needs to be learnt, I have looked at a fairly large chunk of open source project that are successfully funded and i think that is what sets them apart.
I think it is important that users should have a very clear understanding of how you are doing, if you need X money to keep doing this, there should be a pop up saying you need X money on the software and it should be very hard to miss on the website and read me.
Will some people not like that? probably but you can't please everyone and you shouldn't let a vocal minority determines how things happen.