You are paying for 4 screens or streams limited to members of your household. By using their service you agree to their TOS which defines an account being limited to a household.
A Netflix Household is a collection of devices connected to the internet at the main place where you watch Netflix. You may not share your Netflix account outside of your household.
help.netflix.com
If you are sharing your account with someone outside of your household, as defined in the TOS, you are in violation and stealing.
What is your problem with that? Pretty simple stuff, you might not like it but if you want their service and content you play by the rules or you steal from them.