Would you consider "The Communist Manifesto" to be part of Marxism? If not, why not?
And if yes, well, it ends by calling for the "forcible [presumably violent] overthrow of all existing social conditions". That has, in practice, resulted in totalitarianism every time it's been tried.
Now, you could say that there's a lot more to Marxism than that. And you'd be right. But "forcible overthow" is inherently part of it. And as long as it is, a bunch of us aren't willing to even touch the whole package, because we see it as having a bomb in it.