Earlier quoted context omitted.
This is exactly why open borders are not ok. Abuse of workers is NOT an acceptable cost.
Restrictive visa requirements is the reason why workers are willing to put up with the abuse in the first place. Workers have a better shot at demanding a fair wage if they didn't have to face deportation if they spoke up.
What would happen if we opened the floodgates entirely ? Let's be 100% idealistic and just assume everyone reciprocates, China and the like magically become non-dictatorships, and so forth. Rule of law in rural Madagascar magically becomes as reliable as in the central cities of Switzerland. We just equalize the labor market worldwide.
What happens ? Well wages everywhere strongly trend to the worldwide average wage, and benefits. Okay ... so what is the worldwide average ?
1480 PPP$ or 600 actual $ per month. (source: ILO) (note: I would argue there are several reasons why this is too high, for instance this isn't a real average. This is pre-tax income of employed persons, and it's the mean: 80% or so of the population actually earns less than that. Pensioners, kids, disabled ... all earn $0 in these statistics)
And, by the way, you might think, this would make it cheaper to live in those places with high-paying job, but even a cursory analysis of what happens in Delhi will quickly correct you: no it won't. Places like Melbourne would likely actually become more expensive if you open the floodgates.
WHO would this be a desirable outcome for ? Well, there's 3 groups:
1) Obviously for the people currently in high-paying places this would be an extreme negative. They would face 60-70-80% pay cut without a real reduction in living expenses.
2) For people that would immigrate to those places it would be a slight improvement, or a wash. They would, after all, not improve that much in wages, would be far away from where they want to be and have to pay much higher living expenses. (and initially it would probably be a strong negative, as an outsourced wage pays for a lot of luxury in India and doesn't even approach the poverty level in Melbourne, but that's what they'd get. And with wages like that, they wouldn't be able to leave)
3) For the people staying behind this would be a strong negative. A pretty decent portion of the market would disappear (because people drive GDP, more than any other factor), which would mean that most industries would downsize. And that's to say nothing of China's and India's outsourcing sectors. Those would be utterly devastated.
A lot of people in Silicon Valley fall in the category that would benefit from moving (after all, that's why they're there), so they think that if it were to repeat, they would once again benefit. Even if that is a correct assessment (I don't think so, many Silicon Valley positions would be fine with dont-care-about-IT seat-fillers), that is still a tiny, tiny group. The vast, vast majority of people would fall into groups 1 and 3.