I've personally found it's best to just directly ask questions when people say things that are cruel, come from a place of contempt or otherwise trying to start conflict. "Are you saying x?" but in much clearer words is a great way to get people to reveal their true nature. There is no need to be charitable if you've asked them and they don't back off or they agree with whatever terrible sentiment you just asked whether they held. Generally speaking people who aren't malicious will not only back off on what they're saying but they'll put in extra work to clear up any confusion - if someone doesn't bother to clear up any confusion around some perceived hate or negativity, it can be a more subtle signal they aren't acting in good faith.

If they do back off but only as a means to try and bait you (such as refusing to elaborate or by distracting), they'll invariably continue to push boundaries or make other masked statements. If you stick to that same strategy and you need to ask for clarification three times and they keep pushing in the same direction, I'd say it's safe to move on at that point.

As an aside - It's usually much more effective to feel sad for them than it is to be angry or direct. But honestly, it's better to simply not engage. Most of these folks are hurting in some way, and they're looking to offload the emotional labor to others, or to quickly feel good about themselves by putting others down. Engaging just reinforces the behavior and frankly just wastes your time, because it's not about the subject they're talking about... it's about managing their emotions.