This lack of shortage, which I'll call the STEM Surplus, is evident by analyzing the employment of high-tech workers, as described by the recent Bloomberg article and an excellent piece in the Atlantic from earlier in the year. Unemployment rates exceed 7% for the fields of engineering and computer science, in stark contrast to what they would be in an alleged shortage. Additionally, real wages for many science and engineering fields have remained flat for the past couple decades. Science and engineering fields are often dynamic and on the bleeding edge of economic competitiveness, so lobbyists for an influx of STEM workers are able to cite shortages in certain subdisciplines. However, the articles cite the example of petroleum engineering, which was declining two decades ago, have been facing a legitimate shortage due to the expansion of oil fields in the US and Canada (well maybe not for long, with West Texas Intermediate below $55/barrel). The result is that employers started paying more, and suddenly working at an oil rig in North Dakota became a lucrative job. Shortage adverted. The free market works!
The received wisdom of a high-tech worker shortage is propagated by those that benefit from lower wage workers. I'm looking at you, Mark Zuckerberg. A class action lawsuit by Silicon Valley engineers this year concerns the anti-poaching collusion between Google, Apple, Intel, and Adobe. Allegedly orchestrated by Steve Jobs, an agreement was in place between 2005 and 2009 to not recruit each other's employees, thus curbing wages. The tacit admission is that high-tech workers were not properly compensated given their skills. That, and that only half of bachelors recipients in STEM fields find STEM jobs, shows the impossibility of a shortage.
Bringing the STEM surplus up the educational ladder, it is now typical for recent PhDs in the sciences to be employed in postdoctoral positions (hi!), temporary assignments known for their lower wages and lack of definite career path. And this competitiveness and lack of options may compel some postdocs to compromise research integrity to get ahead. A recent report on US postdocs found “junior scientists are primarily treated as cheap labor rather than as participants in a well-rounded training program.” Getting a job in research after receiving a Physics PhD is a tough, and I can attest that less than half of my friends from grad school continued in research, with most of the remainder finding other technical work (still very good!), and others even going on to ruin Wall Street. Physics seems to be one of those fields that still doing pretty well. Examples of those that aren't are the biomedical field detailed by Derek Lowe of In the Pipeline, and featured in Dan Rather's report PhDon't.
All that being said, if you really love the sciences or engineering, I would never discourage you from following your dreams. But knowing what is on the other side of that education is key to making the right decision. And those espousing falsehoods for their own economic benefit aren't helping.