Totally right, pyometra is a major cause of illness and surgery in older bitches that have not been speyed ( it can be fatal if not caught in time and many bitches will be quite advanced before showing obvious symptoms). Speying also vastly reduces to almost nothing the risk of your bitch developing mammary tumours in later life, another common and potentially fatal condition. False pregnancies are avoided and it is widely thought that every bitch will go through some degree of false pregnancy although outward symptoms may not be noticeable. The hormonal changes and emotional upset, which can be severe, that go along with this condition are also eliminated.
Some bitches are a nightmare when in season and will do ANYTHING to escape confinement. They are very good at this when nature calls, and mismatings can be traumatic and expensive and the risk of your bitch wandering into an unknown area is very high.
Too many puppies and not enough good owners is the sad situation we have already put our canines in.