I'm sympathetic to this idea, but I feel like the cruelty has to be part of a means to an end, perhaps to discipline the labor that does make it through in order to benefit the employing class.
You're looking for meaning where there is none. Fascism does not want to make sense, it very intentionally rejects reason and logic. To fascists, force and power is the only real politics. Few people really grasp how deep the nihilism of it is.
There's a sort of twisted reason, though. Fascists need a manufactured enemy to whom they can attribute blame for society's ills -- in this case, the myth of a "border crisis." It's sadly effective too, and somewhere around 70% of right-wingers in the US believe it, many of whom are so ignorant they don't realize they're complicit in bolstering fascism.
Don't forget that fascism is what capitalism degenerates into.
So, follow the money, seek the ones who profit. Fascists themselves are irrelevant, they are basically useful idiots. Look out for those who feed those idiots.
It's simply part of an effort to impose moral beliefs on a world that to them, appears to work without them. Bringing order to chaos. Kind of like the Christian beliefs underpinning such cruelty.
...which is why cruelty is the point. They're getting pleasure out of hurting others. Their pleasure from torment might not be the "true" motivator - I highly doubt the people making these decisions are cackling to themselves like a comic book supervillain while coming up with novel ways of hurting people (though their brainwashed underlings might) - but they get pleasure from power and control, and are willing to pursue it at all cost, which means they do things that are cruel in order to maintain it.
To put it simply, they get pleasure from power and control, which comes at the cost of hurting others. The result is that while cruelty might not literally be the point, cruelty is the end result.
I'd argue it's less about personal pleasure of the act and more about driving votes by perpetuating an agenda that keeps the lower classes kicking down.