Honestly, if you look at Carol Holiday and her relationships to other characters in her life, one thing becomes crystal clear: she constantly refuses, albeit unintentionally, to let anyone "grow up".
Noelle is the most notable example of this, because she's getting a dose from both of her parents. Any time she's in an uncomfortable or threatening situation, either Carol steps in and shuts the entire thing down, or Rudy volunteers to take over the battle on her behalf. It seems like Dess was the main person in her life who helped her actually work through her fears - and without her, Noelle hasn't been doing too great.
Undyne, of course, is the Chief of Police... except she never does any actual policing. Instead of helping her build the skills she actually needs for the job, Carol just does the entire thing for her, keeping her bored and miserable while doing absolutely nothing to absolutely solve the problem.
And then there's Asgore. I find that Toriel tends to be a bit sanctimonious when it comes to other people's business, but she's 100% right that Carol is enabling him. By letting him work at her house, she's helping him stay just afloat enough that he can keep wasting flowers on people who don't need them instead of getting his shit together and selling them to actual customers.
This, I think, casts a lot of suspicion onto her relationship with Kris. It looks like they're working together on this project of keeping the shelter sealed - despite knowing full well that Undyne is inside! And based on the Sword Route, it seems pretty clear that Kris has some severe trauma and fear involving the shelter. So realistically, how much is she actually protecting the town by keeping it closed, and how much is she just enabling them (and herself) to avoid dealing with their trauma?
And most importantly, just what is actually in that shelter, anyway?
Chapter 4 tells us, in no uncertain terms, that the darkness itself is more threatening than anything we could find inside. Sometimes a mask is scarier than the face it's covering. Sometimes hiding in the darkness makes a thing seem more dangerous than it really is. And sometimes a monster's rage and violence is just covering for its massive weak point. (Susie knows this better than anyone.)
When it comes to the Shelter, I can't help but be reminded of the True Lab in Undertale. It's a creepy, mysterious, sealed-off place, linked to a past tragedy, and inhabited by the kind of horrors that even the ordinary monsters of Undertale know to fear. And to their credit, when we get down there we have some pretty spooky experiences, including encounters with those selfsame horrors. It's a dark, dangerous, horrifying place.
And yet... all is not as it seems.
See, the "horrors" in the Lab aren't evil freaks from beyond time and space - they're victims, who fused with their fellow monsters as a result of Alphys's medical experiments, and got locked in there because she couldn't figure out what to do with them. They've just been stuck down there this whole time, waiting for someone to reach out to them, uncover the truth of what they've been through, and bring them back to their families.
To be fair, I don't doubt that the Shelter is a dangerous location. If it wasn't, then Dess would have never been lost, and Deltarune's present day would look incredibly different. But I would say that there's probably more than danger within its walls. It may even, perhaps, contain some sort of amicable figure.
