"they have no function". They limit and control the amount of smoke. Provides a more consistant experience. I read your #4 source as proof. It talks about how cigarette companies tried coming up with a filter to reduce death but stopped because the filters were reducing the taste/experience. That doesn't tell us filters have no use. Include that link it tells us that in the 50s cigarette companies offered filterless and filtered versions. Customers preferred the filtered versions. You made the mistake of thinking the only purpose of filters is less death. Filters prevent tabacco from fall out, better taste, more consistant smoke, nevermind you need somewhere to hold the cigarette as it burns and without a filter you throwaway more tabacco.

#5 Most cigarettes butts are not brown at least in my megacity. White is more popular.

Cigarette butts can take upto 10 years to breakdown at the most.

https://uhs.berkeley.edu/tobaccofacts

Single use plastics take 1,000 years.

One will breakdown in your pets lifetime the other will take a millennia.

We need to ban single plastic use. And perhaps dig a little deeper before making assuming associations (if cigarettes are bad the filters must be destorying the earth / meanwhile the coffee lids you get every morning is really the problem)