We should be legitimately concerned about Sanders winning the nomination. Clinton is a sleaze who would say anything to win. Sanders is a true believer - deep down, maybe not so deep, he wants people frog marched into the re-education camps to have the people changed. She only wants more power.
We should NEVER want a true believer leftist in office. Even if that means rooting for Clinton over Sanders.
I would take Sanders over Clinton any day. I would take almost anyone over Clinton. At least we know where Sanders stands. Hillary is Gumby but much scarier.