They are not "forcing" anyone into donating, anymore than they are "Forcing" them into joining the Gift Exchange.
I agree, there have been times when I would not have been able to make the donation. I also know that during those times... I might not have needed to be participating in such activities... ( please don't grill me for that one ladies, or gents! )
This is a free site! And it is a free site because of the DONATIONS!
And the Gift Exchange is not something that EVERY member particpates in... Its costly, especially if you have more than one dog

I will easily spend 50 to 60 on each of my buddies... I would like to think that the other members in the exchange are just as excited about it as I am... do I expect them to over spend like me?? no, will some?? yes! But do I want someone who can't afford to contribute signing up and realizing that they can't do it because they simply cant afford it, thus leaving someone without their gift? Not really. It sounds harsh... I know. But it protects them too. They won't be put in the position to have to back out.
Just my thoughts....