In previous administrations, people in violation of immigration law were given a court date and released. The new policy is to hold the people in detention until their court date.
I understand that this sounds like a reasonable response for an administration that wants to take a hard line against illegal immigration, and I can understand why right-wing folks would support it. After all, if someone has broken the law, shouldn't they be detained until we figure out who they are and what they're doing?
Here's the problem: If you have to detain people until their hearings, that means you have to house/feed/cloth/etc them. The administration has done a poor job of this and people have died in detention. That's bad policy. If your funding doesn't match your policy, you shouldn't implement that policy knowing it will be underfunded and cause harm to humans.
Also, because parents are being detained, the children with the parents have to go somewhere, so they're being sent to detention camps for children. This is why you're hearing about "kids in cages" more now than in previous administrations. It's a bad consequence of bad policy.
Keep in mind that detaining kids is not new. It's just that in previous administrations, it was a last resort that only happened if a parent was actually a threat that needed detention, and if there was no other family arrangements that could be made to care for the kids. The reason to minimize this type of detention is the enormous psychological harm it does for young children to be ripped from their parents. Due to policy change, this is now common.
If you accept the premise that detaining people pending immigration cases is a sensible policy, at best the policy change caused massive unintentional collateral damage to children of migrants. You could even go so far as to blame Democrats for not funding massive detention centers, which is what the right is doing, but this doesn't have credibility for me. We all know you can't scale up and then be surprised when the servers shut down because you can't pay the bill. In this case, outrage is appropriate, because the administration intentionally put people in harm's way.
If instead you think it's all political theatrics, then you'd believe that the underfunded detention facilities and stripping children from families aren't actually failures, but rather are by design. In this line of reasoning, if enough migrants die in detention and they gain a reputation for being death camps, and if enough children are put through hell of being separated from family, then it will have a deterrent effect on future migration. This may "work" in a technical sense of discouraging the activity, but it's evil. If that's the argument for doing it, we might as well be intellectually honest and just start executing anyone we catch crossing the border. Trump wouldn't be the first leader to put heads on pikes. If we're intentionally harming humans on display as a deterrence policy, it's understandable why that's causing outrage as well.
In previous administrations, there wasn't outrage because this detention and separation policy wasn't in effect.
That policy change is the whole reason people are upset. It's no surprise that ICE and CBP, who carry out the policy, have developed an even worse reputation than usual. It's also not surprising that it's bad for business to work with evil organizations, once the public is aware.
Also, to preempt the obvious rebuttal: Yes, I realize that this policy change was due to public outrage over illegal immigration that put Trump in office. No, I don't think inhumane policies are a reasonable response to Trump's mandate to address illegal immigration.
edit: If you're going to downvote my understanding of this, consider leaving a comment explaining why. I'm pretty sure I've got the facts right.