There is no reason Americans shouldn't have meatloaf for Festivus. Everyone is turkey-ed out from Thanksgiving so a big hunk of meat is not necessarily appealing by time the holidays roll around. I am making lasagna for Christmas. Meatloaf and lasagna are both still filling family meals but bring some change to the same old holiday dinner routine. And to each their own.
Festivus is a fun thing for families to do in order to celebrate the holiday season. That means they should make a tasty meatloaf, even if the family doesn't eat meatloaf the rest of the year. That makes it special for a celebration. Festivus is important because it allows for the annual airing of grievances.
Yes, all Americans should make tasty meatloaf for Festivus celebrations. They should also all gather around the Festivus pole to air their grievances and demonstrate feats of strength to each other. Festivus is a time-honored tradition in many social circles throughout the United States, and reverence should be paid to it.
If people want to celebrate Festivus and make meatloaf, they should do that. If they want to celebrate Hunukah with a menorah, dredil and latkes, they should do that. If they want to celebrate Christmas with a tree and waffles they should do that. If they want to celebrate something else or all three they should.