> What’s so bad about it? We already do it” is a pretty pessimistic take

Not pessimistic at all. It's realistic. We have a finite amount of money and time to make plastic problems better. To make up numbers for an example, if the total amount of microplastics put in the air each year is 1 trillion bits, and if cutting sewer pipes adds 47 bits per year, then saying "What's so bad about it" is actually saying "We have far greater issues to spend our money and time on." and it protects you from wasting that time and money.