Why can non-Christians enter to the Vatican, but non Muslims cannot enter to Mecca?

In my opinion, the Catholic Church should be more strict with that aspect, because many non-Christians go to the Vatican Church, and they do not know what they are doing there. They should have more respect for that place. It is not a place only to take pictures, and that is all. It is a sacred place for Christians, and really important. I think that one of the reasons that Christianity is decreasing, because things like that are important, they do not restrict it.