I have always noticed that when it comes to issues that matter the more mature debate is invariably overwhelmed by name-calling, pedestrian arguments and the like. But I would urge you to please please reconsider this decision. Free speech is important. Without that, you will probably not be seeing the entire context to an issue (English is not my first language and this is the first time on the internet that I am espousing one of my favorite topics). Surely those who (like me) find extreme opinions and violent reactions repellent will be happy to be able to mute keywords, accounts or even block them? Make registration for comments mandatory, for example? I am not from the publishing industry, but I agree with Kittie Phoenix. Removing the ability to comment takes away from the very premise on which you have built this system.
[Having read what I just typed, I realised that I have not said it all but tl&dr, please reconsider with some controls added to the comments section]