You can acknowledge that someone's emotions are valid while disagreeing with them on the content. Here's a template: "It sounds like when I said x you felt y, that wasn't my intention, my intention was z."
The most obvious example is a fear of public speaking. Everyone I know who's struggled with it (including myself) has resolved it through the perspective that it's wrong to be afraid and you've gotta figure out tricks to get over your irrational fear. It's hard to see what a more "validating" approach would look like.
With experience and exposure, we learn how to manage risk and what our limits are. Same is true of learning to swim or learning to drive, but it's not true that a fear of swimming or driving is irrational or unwarranted for someone who hasn't done it often or ever. No, it's completely appropriate.
What would this even mean? I don't see the difference with "suck it up"?
The feeling is real, it's a fact, it could be problematic, feeling shitty in general is problematic, and so ya, if the sight of people laughing, of kittens, of blooming flowers, the singing of birds and all that makes you feel shitty, that really sucks for you, and you'll have to figure out a way to cope.
Depression and other issues definitely cause such feelings of shittinines for things that ideally wouldn't make you feel shitty.
But if others are not willing to help you, then it still seems like a "suck it up" response.
And as a person whose behavior is the cause of someone's feeling of shittinines, what do you mean by: "you're wrong to feel shitty about this"? Are you insinuating that the person is in full control of their feelings and can simply choose to have your behavior no longer make them feel shitty, but suddenly makes them feel good and uplifted?
If so, what's this magic, I'm sure lots of people would love to know. Also, what would they? What motivation would they have to adapt to your shittiness causing behavior?
And on this track, do you really think people are wrong to feel shitty for things like sexual pushiness, inuendo and abuse in a workplace or anywhere unexpected. For pressures to do things, work extra, work over the weekend, etc. For racist or sexist comments, comments and actions that denigrate others for how they look or talk or where they come from, what they believe in, etc.
I'm not being totally dismissive, I think you make a good point, some things are a matter of perspective, but this perspective is important and I think often missed. When someone makes a sex joke for example, they might not mean anything bad of it or try to make anyone feel bad. And arguably, sex jokes shouldn't make you feel shitty. But given a reality where for lots of people this joke is not a joke, but something they experienced for real, a past abuse, a constant stigma, etc., well the joke is a reminder of that shitty thing and causes them to feel shitty.
What is often asked is to stop those bad behavior, and if those are stopped, maybe the jokes about it can fly again, because there'd be no one for whom the joke was just salt on the wound.
In those cases, is "you should learn to have these things make you feel good" really an answer? They logically are bad things, instinctively made to make you feel shitty. So I still think the choices are only what I brought up before.