Austin Frakt and Aaron Carroll have done the heavy lifting of dismantling the Ryan attack point by point. In a nutshell, the main flaw of Ryan's position is that it ignores that the difference between the population on Medicaid and the low-income population without it is that the latter group has no insurance. Medicaid isn't perfect, but for all its flaws, it provides access to healthcare for a population that, in large part, otherwise has nothing.
As Frakt and Carroll point out in the starkest terms:
"Does anyone really dispute that having health insurance is better than not having health insurance? Anyone who does should put their money where their mouth is. Medicaid isn’t
However, as numerous experts have observed, the Oregon study didn't have the statistical design or power to detect improvements in diabetes, heart disease risk,
The most important point raised by Frakt and Carroll is that, if you're concerned about Medicaid's shortcomings and how they hamper its goal of bringing healthcare to low-income people, the solution is to improve the program. Gutting it is the opposite approach.