The cross is clearly the mark of the beast in Revelation. It was the tortuous method of death for the poor throughout Rome and adopted somewhere around the 5th century as an icon of worship. The cross isn't the problem, it's the giving of powers, veneration and worship to it which goes beyond the "mark". The problem is that the cross has become more important than the "living Christ", wherein people give powers to it over the actual Savior. This is why Mormonism doesn't use it. IF the temple in Rome has a cross on the door, it would be "accidental". Undoubtedly, this will be changed before the dedication.
In the Old Testament, the Nehushtan (serpent on the staff), became a source of worship after it's use. It had to be destroyed as people gave it more power than God Himself (see Numbers 21-22; 2 Kings 18:4).