My mother used to tell me, “It’s your tone of voice” when I complained about how my brother was treating me. So first it’s important to be aware of your tone of voice, making sure you’re not sounding superior or condescending. You’ll get a lot less push back if you present the idea as something to be considered rather than something fixed in concrete. Even when there is no other possible way to look at the situation, someone will, and they just won’t hear someone who is telling them they are wrong.
It’s true, though, that sometimes the listener is so sensitive to the subject at hand, that they’ll get snarky anyway, regardless of how reasonable you sound. And then you have to continue to not get in the way–to not take anything they say personally. They may feel the need to rant. You need to feel the need to stay focused on ideas, not on personalities, and never let yourself feel like a target. They’re ranting because the issue threatens them in some way and they just lash out.
Listen and nod. But don’t take the bait. And perhaps say something calm about their obviously having thought about this a lot. “And yet, for the moment, I stand by my remarks.”