It's usually considered rude if it's just out of the blue. If you're making a presentation and it's what's called for, that's different. But in everyday conversation, it's not typically appreciated. I'm sure there are circles in which it's perfectly acceptable, but I assume you're asking about random, average folks.
If you have something deep and relevant to contribute, I don't consider that to be quite the same thing, and there is certainly room for that.