Saying that Sanders is advocating the elimination of private health insurance because he favors Medicare for all is just as inaccurate a saying that anyone who advocates for improving public transit is trying to eliminate all privately owned vehicles.

I'm sure there are plenty of things to dislike about Sanders or anyone else whose political leanings tend toward things like publicly-funded healthcare coverage, it should be possible to come up with a few of them without blatant misrepresentation

That's simply false.

Both Medicare for all and Medicare buy in plans wouldn't eliminate private health insurance.

Private health insurance would still exist under both plans as supplemental coverage that people could buy that would cover things that were not covered by medicare.

The markets would be potentially reduced (drastically with medicare for all, moderately with a generally available medicare buy-in), but it's totally false to say they would be eliminated under those plans.