The negatives are too small to point to the effect but there's no question it exists.
Nice dodge. There are no
net negatives, however, only a gigantic net positive.
What do you see would be a big problem with an open border?
Open borders work between places at a similar economic level. Open borders fail badly between places with very different economic levels.
Again, how? We have open borders, yet you don't see mass migrations of people from West Virginia to, say, California or New York, where there are far more jobs and "very different economic levels."
Anyone that would make the trip to get here for work would be doing so because they can't afford to live where they currently do (which would mean they'd be dirt fucking poor) and as such most of those people would be what we already see; menial workers who would fill the jobs no Americans will deign do.
I'm talking strictly about economics at this point; not about other issues like political asylum.
Anyone with a better economic status either (a) would not have a reason to leave their home country or (b) would just become part of the same job pool as everyone else on similar social levels. Just like it always is.
Within less than a single generation, open borders would simply normalize, just as if we made Puerto Rico a state. Or simply relaxed borders (if open irrationally terrifies you so much) like we had/sort of have now with Canada.
Nothing would dramatically change. No mass exodus from home countries--anymore than we are already seeing--because no matter what, those people would still have to get a job here and compete with other Americans who already have a home-court advantage and still hugely rigged playing field in their favor.
This notion of borders--especially in today's global awakening--is just ridiculous. They have only ever been artificial constructs to define and maintain power.
These last two elections in particular prove that fact. The largest percentage of voters wanted X and the power mongers forced Y instead, through artificial and outdated map lines that don't actually exist anywhere but on paper.
If we simply threw upon the gates tomorrow along the US/Mexican border not a goddamned thing would happen that isn't already happening. Maybe an initial novelty uptick--certainly long-suffering families getting together--and then within
months everything would normalize because people are people and borders are artificial constructs and Mexico would just become another US state, in effect. Just another place to drive to, like if you live in Minnesota and one day decided to drive to Mississippi.
You
want it be special and unique--because that means self-aggrandizement and jingoism and being able to think that the US is special and unique and a shining beacon etc.--but it's not. We aren't. Those have all been deeply ingrained lies from the post World War II days that are
still haunting us, but ever since Vietnam (though a good argument can be made for Korea as the true genesis), it's all been a giant pack of propaganda as evidenced by the fact that idiots had to come up with moronic bumper-sticker patriotism like, "Love it or leave it!" to desperately convince themselves that it's all still good.
Trump has done one very important thing, however indirectly; he's revealed the heart of this country for what it truly is underneath all the bullshit sales pitches and Hollywood/Madison Ave shiny shiny. A bunch of dumb-ass Dunning-Kruger racist pieces of shit who have convinced themselves their shit doesn't stink. Every Trump "rally" is an indictment of Americans, not a celebration.
I think what you really fear the most about opening the borders is that, within a few months--after that initial novelty wears off and it all normalizes--no one will want to come here anymore. Closed borders implies there's something special here to protect. Open borders forces you to realize, it's a huge pile of steaming shit. At least as far as a certain percentage of the population are concerned, both in the corridors of power and those that keep them there.