Pretty sure Dave blocks most people who disagree with him for the space of more than one tweet. People he already holds in high esteem before they disagreed with him might last slightly longer.

I never use such features unless it is really trolling, in which case I expect the flagging system to solve the problem or anti-spam techniques. I don't really like I need protection from people's thoughts, not saying people who want such features do but it's not my thing.