> confirm that they are indeed experiencing that emotion
This is not emotional validation; nobody wants to be told something they can decide for themselves. Instead, they want to hear that it is okay to feel said emotion. When venting to someone, one doesn't want to hear "I understand that you feel that way", they want to hear "I understand why you feel that way". The former is a dismissal (taking the guise of a validation) and the latter is a validation. "I don't get why you feel $EMOTION about this" is the ultimate emotional sucker punch of invalidation from an active listener even though it necessarily implies said confirmation that they feel $EMOTION.
> They're looking for people to share in that anger, sadness, or frustration and confirm that it's a valid response to the situation.
Notably, "sharing" the emotions is not the only way to validate them; I do not have to feel (or even understand) one's sadness for their sadness to be valid. The second part is the only thing they're looking for and it is very unlikely to be false given the appropriate context. From another comment, "the emotional response was valid for the circumstances" is accurate when one understands "the circumstances" to include the life experiences that cause them to have such an emotional response from something that doesn't trigger the same emotions in oneself.
> overreacting to everything and having unreasonable emotional reactions all the time
There are healthy avenues for expressing such emotions as well as unhealthy ones. Validating the emotional response to something is precisely what will allow the person feeling the emotions to calm down and decide on actions that will benefit their situation. If they are invalidated, they will instead spend effort seeking that validation.
> Just going along with it.
Well, if "it" is referring to behaviors and attitudes, then there's an obvious problem (in all likelihood) but that's also distinct from emotional validation. As I said in my other comment in this thread, one can logically say "it's okay to feel that way but you shouldn't think that". I strongly doubt that is the likes of the validation being complained about here. The negatives of the situation being described do not seem likely caused merely from emotional validation. And I would bet with near certainty that the partner they met who got them to choose healthy behaviors did so by first validating their emotions.
> Instead, they want to hear that it is okay to feel said emotion.
That's not the definition the others are using, but this seems to be a game of whack-a-mole with everyone's different ideas about what it means.
That said, I think your definition highlights the problem: By telling someone it's okay to feel the emotion, you've implicitly endorsed the response.
The situations I'm speaking about involve people developing inappropriate emotional reactions that lead to self-harm. When they surround themselves with people who do this "validate emotions" game, they're implicitly gathering consensus that it's okay to react that way. The cycle continues.
It's clear that a lot of people have picked up this idea of "validating emotions" being virtuous and good, but some times what people need is for people around them to explain that their reaction is not actually appropriate or okay.