Should you be allowed to respond and block?

Some mods make it clear, you don't have to interact with people you don't want to, you don't have to respond to people and you are free to block them.

But, you shouldn't be able to use respond and block to "get the last word". Yes, I will be honest I have brought this up and got the response "they don't owe you their interaction"... Ok, but they decided to have a conversation and then decided they get the last word.

Is this petty to be upset about? Yes, so I already know that, but I still am interested in opinions.