I think supporters of the MPCV don't exactly understand its problems. Let's go through them:
1. It is unecessary. There are no BEO missions planned as yet. It makes absolutely no sense to fund a project that has no known use.
2. It is superfluous. There are other vehicles for getting to LEO that have already flown hardware, and look likely to become operational long before MPCV.
3. It is overkill. Currently all US operations take place in LEO, for which BEO capability and a large manuvering capability are not needed.
4. It is an example of a bad system. MPCV is cost-plus, whereas SpaceX and similar are reward-based programs. NASA will pour far more money into MPCV to get some results, than it would pour into SpaceX to get more dramatic results.
Furthermore if the corporate welfare facet of things didn't exist, things would be very different. The whole MPCV scenario just doesn't make sense, and neither does the Senate Launch System. Using a ~70 ton capable vehicle to launch a 4-person capsule to the ISS? What?
It doesn't help that almost all praise for MPCV sounds like an advertisement for Big Aerospace.
And even if going the 'traditional' route is good 'insurance' against the potential failure of SpaceX, for example, PBS (Pork-Barrel System) still isn't a good idea. There are so many better ways to do things, that it really is not funny.