As a 10-11 year vet of steam and with over 280 titles (10 of which are free to play titles) I would back ED on steam 100%. No scratched DVD's or broken boxes, great download speeds at all time of the day and night, great deals on 1000's of titles almost every month and great exposure for any game
And the massive exposure to the biggest gaming community in the world is only a positive.
Now, if FD did end up putting ED on steam I doubt 100% that they would rely on steam for all future logins, it would be just another way for future users to access this product and would not affect all the current users in anyway what so ever.
The only reason you would not want ED to be sold on steam is your own personal tastes/beliefs on capitalism.
I for one want as much exposure for the game as is possible, it would only bring extra cash in to FD and that would on help enrich everybody's experience of ED in the long run.
For me there is zero reason to disagree to having steam as a way for others to access the content FD is offering.
Even bought Roller Coaster Tycoon 3 a few days ago and am throughly enjoying another great FD title (via steam).