A few days ago, someone who had unilaterally blocked me joined my Friends+ instance and stayed there the entire time. Since I was the instance owner, I had the authority to kick them, but because they were chatting with other people they’re close to, I chose to say nothing and do nothing so as not to disrupt the atmosphere.
If the situation were reversed—if I had unilaterally blocked them but they could still enter my instance—I could at least understand that. However, the very purpose of blocking someone is to cut off all connections. Allowing this kind of access to remain undermines the meaning of blocking.