If eBay, Amazon, Yelp, and Craigslist all disappeared today the only people who would be really affected are on the selling side of those services. That would have some ripple effects to be sure, but most consumers would, at most, be mildly inconvenienced.
When you divide the world into "selling side" and "buying side" in that way, you end up defining most of the world as passive consumers. Part of what people like us value about the Internet is the way it disintermediates people, (very) gradually leveling the playing field between institutional sellers and individuals.
To say that new ideas on connecting buyers and sellers are unimportant is to surrender commerce and thus much of modern life to Walmart. Good if you want to pay a lot less for mustard, ketchup, and low-quality lawnmowers. Bad if you ever thought of starting a business or selling something via Kickstarter.
I doubt the fall of Amazon would be as slight as you say it is, but for the others I agree that it might ruin your day/week, but it wouldn't end your life.
The loss of Craigslist and eBay would be deeply felt by normal people. But it sure would be good for huge companies that profit by locking up the retail channel and ensuring that most durable goods are seen as disposable.
