As a Warren supporter, I don't care if she runs on single payer...because, well to be frank, it's not going to happen. The reason I trust her on healthcare is because she has shown she's intelligent, nimble and willing to synthesize new information. I don't think she would refuse to compromise to pass an expanded ACA, public option, or Medicare for all who want it. (All of which I think are good ideas that are far more realistic.) If, through some magical thing, she manages to get single payer through Congress...then she's an even better politician than I thought she was.
I also don't have to agree with every single thing a candidate is running on.The default position shouldn't be that your candidate is always 100% right on everything, and then work backwards from there.