First of all, I didn't realize this was the
DCL forum! Of course everyone thinks it's a great idea! And of course it could all work out.
I just took the OP very seriously. Perhaps her parents' anti-Disney attitude isn't as extreme as it seems to be. And perhaps they would like a cruise. Perhaps they would like WDW. It's impossible to tell what someone else would like.
I guess my take on their Disney-hating is the way I respond when my kids screw up their face before trying a new food "You can't
know you don't like if you've never even tried it." My parents have assumed that Disney vacations are awful, possibly unfairly, which is why we never went as kids. Yes, maybe their worst nightmares will be confirmed, but I am also hoping that if I handle it the right way, toning down the Disney aspects and the crowded activities/lines as much as possible, they will be pleasantly surprised.
For example, if we do the parks, I would go in the mornings and evenings with a midday break to avoid the crowds, only ride the rides we can fastpass, only eat table service, and fill out the rest of the day hanging out at the resort pools, mini golf, or disney springs. On the cruise, we would probably get off the boat and spend time together on land doing non-Disney things every port day, and use the at sea days for things like Palo brunch, pool time, and spa while the kids are in the club, and family activities together like the quiz show, trivia, and bingo. I know my parents would love the live music in the adult areas and lobby in the evenings, and I think they wouldn't mind the shows being disney-based because it is still live broadway-style show and not just cartoons.
We have tried going on other non-Disney vacations with them, and to be honest it is always very stressful because I am given the task of keeping three small children entertained and safe in environments that are not at all catered to kids, with limited success. At least at Disney, I don't have to worry that my kids are not welcome in nice restaurants (I once had a woman come up and tell my I should be ashamed and couldn't I see that my disgusting brats had spilt their milk all over the floor (they were 2 years old, and I asked the waiter for an extra napkin but he was slow!)), or deal with head gashes from hotel rooms that are not even close to child proofed (he still has the scar), or have one child nearly drown because there are no lifeguards at the beach and he snuck out of his puddle jumper when I turned my back (thank god I found him and got him out of the water and he survived). Until my kids are older, I just don't want to mess with it any more.