No, I don't think the internet should be sanitised. But at the same time, I find the MRA shrill talking-points to be of a pretty shallow depth, and, as a group, they're pretty vocally violent. In contrast, I find feminist talking-points to have a fair amount of depth to them. Those feminists who conduct themselves in the shrill manner that MRAs do are just as bad, but when you take those kinds of people away and look at what's left over, it's quite different.
So how should you counter people you don't like? Well, by trying to be mature, and if you fail, trying for better next time. Death threats and rape threats are never okay. Especially if the person in question is not forcing themselves into your life - people go to reddit, reddit does not force themselves into living rooms and makes you read it, nor do many people pay for it.
For the record, I am a white male. I loathe the MRA crowd because they're purely reactionary. Men do have systemic social issues that need addressing, but in general, the MRA crowd isn't actually interested in exploring, discussing, and addressing the issues. Instead, they use men's issues as a weapon with which to beat down discussion that other people are having; there is very little that is proactive in that crowd. For example, here on HN, pretty much all the men's rights stuff has been presented as some sort of counterpoint to a perceived feminist slight... yet these same shrill voices that demand we pay attention to the issues faced by men... never post articles in their own right, only weaponised comments to win internet points.
Threats of violence are never okay unless you're being physically threatened. Immature commentary should never be at the forefront of a social movement, since it's never going to solve root causes and can only provide a superficial salve. These things are destructive, and are all about making the other side lose - an ideal outcome is a win-win situation, though that's not always possible, of course.