(*) Ignoring someone isn't as frequent of an action as (let's say) sending merit.
Are you sure about that? I've seen enough posts from people who can no longer view their Ignore list, because it's too long doesn't load before it times out. Most users haven't sent that many sMerits, and I can only hope people use the Ignore list when they read crap. I know there are many more posts that aren't worth reading than there are good posts, so it would make sense to use the Ignore button a lot.If anything, it may be undervalued. We're now going from the suggestion to bring back the glowing-hot Ignore button (to make it easier to recognize and ignore shitposters), to making it harder to ignore someone.
I'm pretty certain that if the SMF mod that (I think) the user-ignore feature is based on had included a confirmation dialog from the start, then any proposal to now get rid of that would probably be met with "What are you doing? Leave it alone!" 
Okay, here's one: the "delete" button has such a confirmation popup. I'd love to see that removed! I now use my middle-mouse button on the delete button (this deletes the post without popup while opening a new tab which I can click away). I think I've done that accidentally only twice. I'd be totally fine to never see any confirmation popup ever again.