Jesus, that paralympian thing is insane.
You can basically take this phenomenon to any extreme conclusion, any group can take issue with anything. They're actors, they get paid to put themselves in other people's shoes, play other people.
If you've got a huge-name genuine-amputee/prosthesis user with Dwayne's marquee-value, sure, right, go for your lives, give them the role.
That person doesn't exist though. He's not doing anything wrong by taking that role, if anything he's probably doing net-balance good by getting people who wouldn't usually think about the difficulties these people face exposed to it.
What, military guys with PTSD are going to start saying "hey, action-movie guy, how dare you play a returned vet with severe shellshock?!" Or "British stage actor guy, the balls on you for playing an Irishman! Your ancestors screwed over mine! Irish people play Irish people only!"
They might as well start. Consistency's sake and all.