That is a terrible argument. Let's take it to it's logical extreme:
Lady crashes car doing something stupid. The seatbelt was installed improperly, and in fact, the company uses a process of installing them that nobody else in the industry does. They are even aware that the seatbelt will fail under certain circumstances, just as McDonald's was aware that they were serving coffee so hot that it couldn't be safely consumed, whether inside a car or not. The lady loses her case because she did something stupid, and the car company issues a statement saying cars aren't meant to be crashed.
That is your logic in all it's glory. McDonald's offered an unsafe product, was aware that it was unsafe, and continued to offer it anyways. This lady gets hurt and asks them to cover her medical bills. They refuse, she has no choice but to sue. This is a textbook example of corporate negligence.