Yes, it is generally useful to talk to people you don't agree with. But talking means that your exchange follows a certain rules. There are things you can't do when talking, such as throwing a punch at the person you are exchanging information with.
I would argue that following certain rules of reason and debate is a fundamental part of what defines talking, such as: staying on topic, not using a plethora of unsubstantiated claims and immediately placing the burden of disproving them on your conversation partner, not screaming and raising your voice, not conflating completely separate issues, not oversimplifying the world to be black and white, etc.
I would argue that the right-wing rhetoric has, for years, been undermining making talking possible by rewriting the social protocols of what is acceptable in a discourse.
It is absolutely NOT useful to try talking to a person that is not talking to you.
It wouldn't take long (say, 5 minutes on /r/TD) to convince yourself that there's a wide class of Trump supporters are not talking. They say things that will make you angry and want to argue, and that's the endgame.
I think many of us have had these conversations, where one wants to scream: "You can't say this! You are basing your opinion on nothing but that's what in your head, so no, your opinion does not merit being listened to until you at least try to find out what's actually going on!" How many of us would plead the other party to put two and two together, and and be baffled why they would try to simultaneously - and furiously - throw opinions at you that contradict both logic and the real world? (If you haven't had that experience lately, go find a religious conservative among your Facebook friends, and try holding a conversation on the subject of providing contraception and funding Planned Parenthood).
The way such conversations go is the result of a successful attack on reason conducted by the right-wing political apparatus.
These attacks on reason made talking impossible.
The worst part is that they are infectious. Once you engage in the reason-less farce, you will lose reason, too, simply because it becomes useless in the pseudo-debate you're trying to have. It's hard to resist getting angry and pulling things out of thing air if your opponent is doing the same. So yes, you will find some of your liberal friends doing the same. Losing reason is easy.
And this loss of reason, in effect, is the crown achievement of the political right.
It's not just my opinion; the attack on reason by the Republicans in the US (and by Putin in Russia) has been well-documented. Please consider the following articles:
http://www.slate.com/blogs/bad_astronomy/2016/06/30/donald_t...
https://www.theatlantic.com/magazine/archive/2014/03/the-war...
https://thinkprogress.org/when-everything-is-a-lie-power-is-...
Going back to the premise, my conclusion, based on too many hours of personal experience:
For one's sanity's sake, it's often worth to avoid trying to talk to people you don't agree with.
This will change once we can talk again. Here's to hoping that this moment will come.