First, they are not the only organization that does this on "public land"......
Outfitters, hostels, restaurants, etc...commonly do it. So why is this any different?
Guess you've never heard that nothing in life is for free.....
Secondly, if you were doing this to convert people to Islam, I would have no problem with it.....knock yourself out.
Thirdly, there is no such thing as "freedom from religion". Your freedom is that you can have a religion or not. Just as your "freedom of speech" is not the "freedom to be heard", because we don't have to listen to you.....
Like I said......eat/drink their food, or pass on by......your choice.