~snip~
You are making a connection between your online privacy and the use of AV, which has absolutely nothing to do with each other - because AV should protect you from viruses/malware/spyware and not protect your privacy. If you want to somewhat protect your privacy online, then use a VPN or even better Tor, and don't reveal your personal information unnecessarily.
I believe they become related when the downloaded infected AV starts digging for the important files on the infected computer. I agree that AV should protect our unit from viruses or any unwanted files but if it comes from the unofficial sites then the worst thing can happen.
I don't know what to say about your claim that AV can easily become a virus, but I guess you have your reasons for thinking so...
AV can be easily an hacker application if they are downloaded from unofficial sites. As far as I know, @OP give links of those AV injected by malware comes from the unofficial one tricking naive people who wanted free Antivirus. So people must learn to verify whether an application comes from the official sites since any hacker can just modify any AV and upload it elsewhere.
Do people still use antivirus? This is new to me because I have noticed that people do not care a out antivirus again since antivirus am easily because a virus. I take my privacy very serious and that is one of the reasons why I have decided to stay away from using antivirus because they are majorly the problem most of us might be facing when using different gadgets.
We can always stay without using an antivirus if we can maintain our privacy.
Many people still use antivirus and internet security especially when there is a huge risk when browsing the internet. Internet security can halt the access to a suspicious site when an AV can block the download or installation of any file that is infected by malware. It serves as extra layer of security and it does not hurt if we deployed one.