Having people enter the US at ports of entry is not horrendous, per se. However, what about those who allege political persecution by governmental entities in Mexico or Canada? And then there are ports of call. It could happen and probably already has in our history. I just don't know off the top of my head and don't need to research it to substantiate my point. Whether it's happened before or not, the point is still valid.
Regardless, this whole "border-wall" approach is the wrong way to go about fixing immigration issues. Yes, until things are fixed and even as part of the final solution, screening immigrants is necessary under our secular condition. However, the focus, the emphasis, right now and going forward should always be fixing the reasons people want to immigrate in the first place.
Central America is riddled with problems that have been exacerbated or even started and caused by US foreign policy toward the region. The same is rightly said concerning other parts of the globe as well.
The focus of the US should be to help convert bad governments around the world into good ones. That means ending US support for dictators of all stripes. We can't support dictators just because they allow US corporations a freehand. We must support grassroots democracy even if US corporate interests don't like it.
As for arguments that migrants are or aren't dangerous, well, some certainly have been. Holding up the US average rate of crime versus crimes committed by immigrants is not a valid argument for open borders. Hopefully, we aren't seeking to maintain our current level of crime but rather are seeking to reduce it. It's vastly easier to focus upon citizens and a smaller population in working on that than it is when allowing in those who have not been politically socialized for it. That's why working on helping other nations to become grassroots democracy is the right first-principle and needs to start right now.
None of this excuses a lack of compassion, a lack of charity, a lacking of giving and sharing, so those who enter the US can heal. What it does all mean is that the US needs to put its own house in order regardless. We too need a grassroots democracy. We don't have one right now and never have. The US governmental and political systems were designed to create and maintain an elitist, anti-grassroots-democratic system. That's been our problem all along. We need to fix that immediate.