You shouldn't. Antivirus is a relic of the early 2000's.
http://decentsecurity.com/about/ (This entire website)
https://www.microsoft.com/emet (for Windows)
https://paragonie.com/blog/2015/06/guide-securing-your-busin... (basic web security advice for non-technical people)
You don't need AntiVirus.
One obvious difference is that the consequences of mistakes can be higher for STDs then for infected computers, but that's the analogy.