That is not a viable option for everyone; there is not much out there still left for the people. Nor will those who have invested their energy be told to buzz-off.
In an age where technology allows anonymity, people can come back again and again under different pseudonyms. It’s not, from a forum administration point of view, possible to restrict certain individuals from joining w/o blocking everyone. What is possible as Nagalim mentioned is they delete your account and your writing. What a shameful act! I think only morally bankrupt individuals would stoop to this level because they feel they need to use dirty tricks.
IMO, the only best way to address problems is to actually have meaningful, intellectually honest discussions. Citing the individuals who bring these thoughts to our attention as anything other than though-full and useful members of our community is not going to help.
Given the combination of 1) impossibility of total banishment and 2) the legitimate issues raised, i think a sensible course of action should be clear…