[Edit: Please don't interpret my comment as suggesting I think this is a good idea. If you check my posting history, you'll discover I'm an outspoken proponent of open borders.]
Even so, if my country started to structurally refuse entry to foreigners who had - at their expense and with considerable documentation requirements - obtained a visa in the legal way I'd be quite upset and in fact highly surprised.
See, even though a visa is not a guarantee the general rule is that they are not withdrawn capriciously and if you do that you risk making people from other countries wonder if it is worth applying for a visa in the first place.
I have heard of the US refusing entry to people with visas. I know someone this happened to, in fact. But since Trump (or other similar villain) wasn't the president at the time, no one really cared.
That's along the lines of if something happens to one person it is a tragedy but if it happens to a lot of people it is statistics.
The numbers are now high enough that it has become a statistic, and one worth noticing. It also draws attention because the list of 7 countries could easily be expanded (on a twitter inspired whim no less).
It's the capriciousness and the uncertainty coupled with the numbers that make it an item, not because it is Trump or someone else at the helm, if Obama would have done this it would have resulted in much the same level of pushback.
https://sethfrantzman.com/2017/01/28/obamas-administration-m...
Obama did something similar in 2012 to little protest.
http://content.usatoday.com/communities/theoval/post/2012/03...
Again, I'm against this. But this is hardly unprecedented or shocking - the only shocking thing is that one of our cultural enemies won a popularity contest and then did this.
In particular, nothing in TTPA barred entry to people who have helped American armed forces, or legally enrolled students from those country, which this order does. Again, not by authority of TTPA, but under INA. Taking the executive order at face value, the executive can ban any and all countries. The fact that they used the list from TTPA is political convenience.
I can only imagine the calculus going on in the conservative party at the moment, it must be something along the lines of 'damned if you do and damned if you don't', when the music stops playing it will get ugly.
Maybe I'm being presumptuous, but do you have a Western passport? If so, that buys you a lot of goodwill when it comes to entering a country.
People with passports from developing countries often have a hell of a time getting into the US, even with a visa.