When blocking a forum user doesn't work, is when the blocked user replies to the member who now cannot read the reply. The blocker has no idea if the reply is more topic-damaging, or more in-agreement with blocker.
What happens next is the blocker begins to read the blocked-one replies to the blocker and becomes forced to respond, in self defense of the topic. In other words, the blocked one could out-smart the blocker on the topic and the blocker can't do anything to defend themselves...... without reading the response from the blocker user first.
I've been doing major league baseball messageboards and firearm forums since 1999 and witnessed many times that blocking active members that post a-lot, just doesn't work as advertised. Then,. to make matters worse, once the blocked one finds out he's being blocked, then any raves expressed to the blocker turn into rants afterwards.
My opinion is to never block anyone, even if you-both can never seem to agree. Just report to the moderators anytime someone berates you personally. Let Moderators here deal with solutions.
