"If you are violating a patent, then it is perfectly normal, and expect, for the patent holder to demand you stop or pay royalties."
That depends very much on the industry and the market conditions. Patents are often acquired with no intention of ever demanding anyone stop. They are sometimes acquired, especially by young startups, to add value in the eyes of investors. They may be licensed in conjunction with consulting agreements and transfers of know-how where the patent really does serve as closer to an advertisement than what the licensee is really buying. They are also often acquired for "defensive purposes" with no intention to ever sue unless the other party sues first..