But also, in defamation law, just because you couch an accusation in the form of a question or opinion doesn't mean it's not defamation.
If a reasonable listener is likely to take your question or opinion as a "statement of fact," then it's defamation (if it's also false and defamatory).
Whether a question or opinion is really a false "statement of fact" is for the jury to decide.
You don't get off by saying, "In my opinion, Joe Smith met the child Mary at the playground at 3:13 p.m., which I can see from my window, and raped her with a butter knife. But hey, that's just my opinion." Wink, wink.
That's so specific, a jury will regard that as a "statement of fact," so it better be true.
You also don't get off just by throwing up a question mark.