You don't have to be back by the return time on the fastpass. You can come back anytime after the return time.I have already made clear my thoughts on the flaws in the Fastpass system a few pages back. However, I will just say you get what you paid for.
I pay to stay onsite so I don't have to keep checking the time to make sure I make it back to the ride by the return time. I pay to stay onsite so I can get on almost any ride in either park whenever I feel like it without having to wait in a line. I pay to stay onsite so I can ride my favorite rides over an over again. Riding Dr. Doom 10 times in an hour? I could NEVER ride Tower of Terror 10 times in an hour...it would take more like 4 or 5 hours.
My other issue is the fact that Disney guests stay at these Deluxe hotels and get NOTHING for it other than a "nicer" room. Your at Disney! How often are you sitting around enjoying the pictures on the wall in your room? At least at Universal I pay to stay at a Deluxe style hotel, and I get the royal treatment for spending the money. You get nothing different between Disneys value hotels and the deluxe hotels...it really surprises me that so many people will stay at deluxe hotels. If Disney started doing what Universal does and gives all Deluxe hotel guests an unlimited "fastpass" system, I would be coming right back to Disney and staying at Deluxe hotels for the perk. I have been spoiled by Universal and never having to wait in line, that I don't think I could manage Disney during the summer anymore knowing that if I would have gone to Universal, I would not have to wait in hot, annoying, hour long lines.
You know what you are paying for when you stay Deluxe at Disney. How does that have anything to do with whether their fastpass is fair? Don't stay onsite if it's not worth it. Not a valid argument.