You talk a good talk, but almost everything you example is based on manufacturing. Seats and cushions, or trade of seats and cushions. What the OP was referring to was those jobs that produce the same "seats and cushions", but at a lower price. Software development is not manufacturing and when you start to supplant the IT workforce in your own country by one in anothers you are causing two major drags upon your own economy.
First, you put people out of work that more and more are unable to find work since their jobs have been moved. Again, we are not talking about improved productivity in moving jobs, just reducing labor costs. Now that you have these local IT workers out of a job they become a burden on the government (unemployment), the healthcare system (inability to pay), and if long term, welfare or prison. Along with that you've taken a well paid person who pays taxes and spends money into one that uses taxes and has no money to spend.
Second, even if that person gets a job, it may be for less money. Given that, it means a reduction in tax revenue directly through employment taxes and a reduction in tax revenue in reduced spending. Both hurt GDP since they are more inclined to buy imports at a cheap price (how ironic) then products made in country. Trade deficits increase which further drags the economy down for the masses.
There is a difference between moving manufacturing jobs (bad as that is, see #2) and service jobs. IT is a service industry and there's not increase in efficiency by moving jobs over seas. Actually it tends to hurt companies long term since the service returned most times in lower quality and thus it costs more to fix. H1B, as abused today, hurts the GDP, because it allows companies to negotiate labor pricing down which impacts the buying power of the american worker and many of the H1B workers shipe their income back to families overseas, meaning it is not spent locally and not helping supporting businesses thus a drag on GDP.
Finally, when jobs are moved overseas, mainly higher skilled, those people still live in this country. It is not like the person disappears. Way back when there may have been room for displaced people to move and start over, western expansion was a prime example of that transition. However today there is no new frontier and technology is pervasive so take a manufacturing job or IT job away and it creates a vacuum that cannot be filled, yet the person stays. We have serious economic unrest, because decisionmakers think like you and never factor what to do with the people left on the side of the road. As exampled by history, unless you tried to kill them off (and that never works), they eventually rise up and try to kill you (that does).