This. I lost a lot of respect when Firefox complained that something was wrong, and it turned out to be Avast doing a man in the middle attack to 'protect' me on https websites.
You really have to be careful what you check to install or enable when using antivirus software. I think Windows 10 does a pretty good job without any extra software, but there are people that still torrent movies and open EXE files from whatever website they access. Sometimes teenagers or older people. Who knows what they are putting on their computer, and I imagine a lot of it is able to bypass standard AV products.