The current political reality is that about 1.2 million immigrants are accepted legally into the US every year, a number that falls far short of demand. The current system is generally based on family reunification rather than work force needs (such as skilled immigration).
Silicon valley employers, ostensibly unable to hire the workers they need (under the terms they feel are acceptable) from the citizens who were born here or immigrated through non-work related programs, have lobbied for the power to bestow "front of line" privileges on people (usually STEM workers) they wish to hire. This is an unusual request (and substantial expansion of corporate power into the immigration system) that they justify by claiming that there is a shortage of these very highly skilled workers, a shortage severe enough to cause harm to the US economy in general.
This is where it starts to get complicated, because if you change the rules only for a small segment of the workforce (such as proposals to staple a green cart to STEM degrees but not dentistry, law, MBA…), you may end up creating market distortions that reduce the attractiveness of engineering or software relative to the other fields highly educated people can pursue (provided those people already have the right to live and work in the US). When you consider the skill it takes to be a good software developer and what they could earn in some other field, I don't think that the evidence supports claims of a particular shortage.
Take a look at the US News Best Jobs salary data some time, and focus on salaries in high cost regions like SF. You'll find that while programmers are reasonably well paid, in SF they earn only a bit more than dental hygienists, and quite a bit less than registered nurses. I also think that career stability and long term prospects may actually be much better in other fields. In short,I think that the aversion to software development among people who already possess the right to live and work in the US may be rational and market based, and that getting the government involved will simply forestall the market signals that would get more people interested in this field. Pay and work conditions (you make about as much as you would have with an associate's degree in a health related field, work in a giant open office with back visibility, in a company that may discard you when you get older, perhaps demanding that you train your replacement) need to improve to get more people into programming. Why should we tinker with the immigration system to allow business as usual, when clearly something needs to change?
Just to be clear, I do think that openness to international engineering talent is a critical factor in any countries workforce, and I do favor some kind of skilled immigration program. My big difference is that I also see a potential risk to the domestic pipeline through these market distortions.