First of all: please let us separate this. What one believes isn't science. Science does not care for your (or a mollusc's) feelings. It cars about what's the provable truth (except when the science is psychology or behavioral biology, then it cares very much about your or the mollusc's feelings). So if it can't be proven, science will ignore it.

Secondly: there is something you need to take into account herey and that is cognitive abilities. It doesn't matter how the behavioral response of an animal is, if said animal lacks the horsepower to interpret those feelings. Do you feel bad for a computer when it encounters an error? Of course not. Why would you? It lacks the cognitive ability to suffer from that error. Same goes for animals. Dies it feel compelled to be in a group? Maybe. But does that mean that inside the animal's head it goes "oh, finally a group, I'm so safe now. I was really hurting being alone and all" or is there just a little mechanism that goes "Func_Search_Group exited with status code 0"?
We don't know. All we know is that both exist. Dish forming swarms show more of the latter, while dogs display more of the first. if there is no psychological response to any given feeling, we can't attribute emotions to it. Furthermore, all of this is only applicable if we assume that the way our mind works is the only way. Some animals might have a psyche that's so far removed from ours that our metrics just don't apply. We don't know.

Of course there are tons of animal behaviors we wrongly Attribute to instinct or reflex when they are actually emotionally driven. Yet we don't know what those are, so we cannot just run around and play pretend because it makes us feel cozy.

We humans are actually a good example of that. At birth, we are just a bundle of cobbled together reflexes that get replaced by cognitive ability over time.
I'm holding my three weeks old toddler in my arms right now and since he is actually a human,. observing his behavior is relatable to menand easy to interpret since he's hard wired to communicate everything bad by crying immediately.

Yet, there is tons of behavior he shows that's actually reflexes and his brain will not start the same reaction as a more developed human brain would.
Take shock as an example. He is literally impossible to upset by shock. If he feels like he's falling or something else catches him by surprise, he'll react by the so-called Moro reflex and try to grasp anything in his reach. It's the same reflex we see in chimp babies. It's meant to make the baby cling to it's carrier's fur. Yet, he himself doesn't react at all. He looks midly irritated at best, if he doesn't just continue sleeping and that's all. His brain does not process this shock emotionally like we would, yet his body goes into full blown panic mode, desperately grasping around. No suffering, no anxiety, nothing in terms of emotions at all (and believe me, a baby will not hide those. He cries if his intestines are starting to digest the milk he just devoured)

If this kind of disconnect between behavior and psyche is common in humans, it is likely to be common in other species as well, especially when those species lack the ridiculous large and energy hungry brain humans have decided was a good idea?

Is it actually the scientist neglecting the mind of an animal or is it you wishing for a mind to be where there is none? The answer is somewhere in the middle.

Oh and the cat example: that's a result of the very mistake you made: people have somehow collectively decided that cats lack any social behavior and thus anything they do that looks like socializing must be something else, in spite of evidence to the contrary. Cats absolutely do socialize just with less to no empathy for their friends. That's why we can only call true what's observable.