First of all, tech has always destroyed jobs. Tull's seed drill dramatically reduced the labor required to sow fields. Water-driven looms dramatically reduced the number of weavers. No one ever foresees the new jobs that will emerge and everyone always laments the jobs being lost. Secondly, Detroit collapsed because it hid behind import quotas and continued to manufacture junk; when the import quotas were finally relaxed, people rushed out to buy automobiles that weren't lumps of rubbish. Silicon Valley isn't hiding behind import quotas; ergo the analogy is 100% flawed. What may harm the Valley is the dearth of grownup venture capitalists; the current crop are mostly MBAs who came straight out of grad school and became Associates. In consequence they have zero experience of real-world issues, which is why they throw billions at companies that have zero path to profitability in the hope that an IPO will let them cash out before people realize these unicorns are financial black holes. But even this stupidity - which we saw in the dot-com bubble - is likely insufficient to cripple the Valley. Even the repulsive Zuck-style frat boy culture is failing to kill the Valley, and that's something much more toxic and destructive than any exogenous factor we've seen so far.