Antivirus: yay or nay?

[Xiahou]

I'm a long-time A/V user, in the last few years using Microsoft Security Essentials specifically. Lately, I've noticed that MSE has been bogging down my PC post-login. Eventually, the problem goes away but my PC is very sluggish until MSE is done with it's gyrations.

To the point, rather than trying to make MSE behave, I'm thinking of dumping antivirus altogether. Does anyone else run without A/V programs? I can't remember the last time MSE actually hit on anything. My pfsense firewall performs some IPS functions that would block/alert on malware. I use NoScript & Ublock Origin on Firefox. It seems like I'm pretty well covered even without antivirus.

Someone tell me why antivirus is anything other than a waste of computing resources at this point?