Emotional validation can be great. Everybody likes to know they are heard, understood, and that their emotional experience is valid. When a hurting person has someone to lean on and talk to, who can validate their pain and let them know they aren't crazy for having those hurts, it can be instrumental in that person's healing.
But there is a limit to what validation has to offer. There is a limit to validation's effectiveness. The issue with emotional validation is that our emotions about things are tied to us, and we sin. Therefore, there can come a point where you just have to tell the person, "I've listened to your hurts so that you know I'm in your corner. I've cried with you, hurt with you, and felt frustrated and angry with you. But now I'm really just listening to you complain about and criticize people, and that has to stop. I'm not going to sit here and let you sin and expect me to help you."
Emotional validation is helpful in careful doses. It can help a person through a tough time. It is a foot-in-the-door toward establishing trust and partnership. But validation at the expense of the truth can just be enabling someone to continue in sin.
"Hey, I understand that you feel very frustrated about those people, but right now you're just sinning. They haven't actually sinned against you. You are expecting me to tell you that it is okay for you to act like this, but it isn't. Sorry."