There's a level 1 contrarian argument that "masks don't work" which is very similar to "border walls don't work."
In both cases the theme goes: "Physical barriers are not invulnerable, so they are not a useful part of a mitigation strategy".
In both cases I believe this is special pleading. People who make the argument re: immigration actually just don't like the wall because it's against a group they like (immigrants). People who argue against masks for coronavirus are trying to argue something similar - that the virus isn't as bad as people make it out to be, and isn't worth defending from.
There are some obvious problems with both arguments - mainly, that groups which the arguer probably approves of demonstrate that they disagree with the argument. But the arguers rarely address them:
Imagine you challenge someone to spend an hour with someone with coronavirus: would they really voluntarily not wear a mask?
They're also vulnerable to reductio ad absurdium. Imagine someone who somehow is wearing 100 masks. There are so many their entire body and face is covered, and someone with coronavirus is 5 meters away. Would they be safer in this situation than if their entire body weren't covered? Obviously yes, because water droplets leading between you two would be more likely to be caught by the masks, rather than directly contacting your skin / mouth.
Now imagine you only have half as many masks on - still feel safer? Obviously, yes. Just keep lowering the number of masks. Their value must be continuous, and won't decay to zero until there are zero masks.
So, admitting that a hundred masks are useful implies that one is also useful. And I don't think anyone would admit that a meter thick covering of masks is not "more effective than air" at preventing the spread of physical particles.
People often argue this based on "pore size", that some masks have holes that are bigger than the virus so it can fit through. Okay imagine I gave you an N95 mask (which has holes small enough to block viruses). You'd be happy. Then imagine I poked a single microscopic hole in it, big enough for a virus. Would you then not want to use the mask? The bad masks with large holes are exactly this - they're effectively N95 masks (on the solid parts) with tons of holes in them. But the parts that don't have holes are still effectively walls!
It's funny that people who say the wall won't work don't address historical examples of walls that worked: How about the Berlin wall? This example shows what's really going on. The Berlin wall did work, but they hate it because it was cruel, and the border wall takes on those connotations of violence towards wall-crossers, which they hate, which leads them to hate the wall.
How about the border walls Israel builds? Why are they doing that, if walls don't work?
None of this is meant to show that I favor the wall; just that the arguments against it are not valid.