There indeed is such a thing as a “bad known” and a “good unknown”. And not so surprisingly customers usually prefer the former. Let me illustrate with a true incident. So it once happened that many moons back one of my customers inherited a particularly unpleasant “runaway” product version. It so happened that a previous vendor had installed a particular version of an open source product. Over time this vendor added extensions and customizations to the product. After about a year the vendor was replaced and me and my team was tasked with the maintenance of this product. We immediately decided to install the latest version of the particular product since it had a number of new features and bug fixes (some customizations that the previous vendor had to implement were now out-of-the-box features). To our surprise the customer opposed this plan as they did not have a firm grip of all the custom features/extensions that the vendor had implemented and they feared that simply switching to the newer version of the product may lead to their users discovering missing functionality post production.
No one should dispute the fact that the customer had a weak process; they should have had a much better understanding of all the custom functionality that the vendor was implementing. This situation forced us to keep the new product on the QA environment for many more months than we would have liked while the users were comparing features against the old product and identifying any missing functionality. The customer was willing to invest time and money to keep the old product around even though they knew the newer version was so much better. Given the choice between having a buggy version of a product but one which they knew what they were getting (bad known) versus a newer more stable version but with the caveat that it could have missing functionality compared to the older version (good unknown), my customers choice was pretty clear.