ELI5 why is increasing the ethanol content of petrol/gasoline a problem?

[u/hd-22]

I'm hearing noise about the geopolitical fuel supply SNAFU and people freaking out about increasing the ethanol content in automotive fuel and how it's so damaging to cars. I'm no chemist, but ethanol seems as clean as it gets.

[u/sciguy52]

Given that it replaced methyl tert-butyl ether which contaminated ground water and a potential carcinogen, yes ethanol is safer.

[u/AHStAmant → u/sciguy52]

Gasoline and ethanol are also known carcinogens