The Flat Earth Society has members around the globe. What I wanna know is why isn't there a Flat Mars Society?

There are/(would be) 2 main reasons:

1) Mars is a smaller planet, it does not look so flat to someone standing on it
2) The atmosphere on Mars is much thinner. dust have an easier time settling and restoring the good transparency of the air. You can see as far as the eye can see. And that includes seeing if the horizon have cut off the lower 5 inches of a measuring stick 'over the horizon'. In contrast Earth air is soupy with water vapor and dust and life, On earth seeing something cleary a mile away is a rarity.

That sounds funny...'flat Earth society with members around the globe'.

I suppose that from here, all other planets appear as a circle either in drawings or through a telescope no matter what time or angle, other than when the moon is not full, so no question about those being a sphere, globe, round circular or whatever. Here there are hills and plateaus and perhaps they cannot perceive that gravity would keep people from falling off of the other side? 
Not really sure, I don't get it.

mars is a myth made up by the romans

I'm going to have to level with you for once ....and say I'll not Disc'uss it....:(