The 'we can't afford to do it, I wish we could' message seems to be increasing as an argument against any sort of reform. This is a fairly clear argument that it is the opposite; we can't afford not to do so.
Here is a familiar picture showing that deficits are increasingly driven by Medicare and Medicaid...this one with about 25 years of past data. It helps illustrate the effect of the baby boomers retiring, and how much more profound the effect is on Medicare and Medicaid than it is on Social Security (because Soc Security doesn't have a 'runaway inflation problem'). This picture should keep you awake at night if you are younger than 50.