Well the first step in taking the Devil's Advocate side of the debate is to fulfill that title role. Make your opponent's stance look like the asshole one. Twist it.

- Start with mentioning that the physically and mentally disabled are people too, and as such, don't want to feel belittled. The kicker: The mentally disabled don't want [and don't need] to feel pitied and coddled by being given a free ride. They want to work for a living, be treated with the respect that comes from hard work, not handouts. This goes hand in hand with saying that some of them are even more qualified and harder working than the non-disabled in many fields.

Now that's an asshole move, but it's what politicians and pundits do every day. Spin. You need to say the above in an even more schmoozing manner. I didn't do too bad, but that was written on the spot. A little more prep makes it even more convincing.

The key to playing devil's advocate is to think up everything that your opponent would say, and make it look like the terrible thing. You don't have to come up with your own arguments, just knock down each of theirs. Why? You can always one up them with this next point.

- Funding not spent on financial support mentally or physically disabled people can be spent elsewhere, as the disabled are more than capable of earning their own, on other projects such as general education, disaster relief, etc, etc (other things that no one denies are useful).

Try to segue into each point, making all three of them related. It makes them even more solid. I can't think of a third one right now, but those two are a good start.