There should be limit to how many people you can 'block', if you need to block more than 5 people (or 10 max) the problem is probably you.
The 'ignore' feature should have no limit. You should be able to ignore as many people as you want, just as you can at the moment.
The 'block' function does ruin the site for other people.
When I create a thread and someone who has me blocked replies to it. And someone else replies back to that blocked reply, and now and my own thread no longer makes sense to me.
The main culprit seems to be user 'maxinger' who it appears has many people on block but can still reply to threads started by people he has blocked.
Another thread starter also noticed this, see this post.
https://www.elitetrader.com/et/threads/anyone-else-self-sabotage.379309/page-3#post-5959232
I noticed the exact same thing, he was replying to my threads as well, but has me blocked, he did not reply to my posts directly, but to other people on my thread, and i could see their replies back to him, but not his posts.