You are not wrong that polio spreads through feces of infected individuals, your intestines are where it usually replicates. I might add though that in the 20th century counterintuitively it was the improvements in bathroom hygiene in the western world that have caused the high ratios of polio induced paralysis. Mostly because with really bad bathroom hygiene, even babies get infected with the virus, who still receive antibodies through their mother's milk and are protected by them. The immune system can deal with an infection and gain immunity in a safer environment. Now, in places with improved bathroom hygiene more children get exposed at later ages, like e.g. the toddler age. At that point, polio is way more dangerous as the immune system is not helped by the mother's antibodies.
https://nextnature.net/story/2014/how-modern-sanitation-gave...