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Of course, there are ways to relax this, but it's always a trade-off -- less security, more performance.
Believe me, with this kind of problem I started to believe we really want that trade-off. What's more important for me than thorough scanning on boot-time (logging into Windows time), would be good and if possible (of course) faster on-demand scanning engine. We all pretty much do scan our systems on regular basis, so scanning with such an intensity on boot time IMHO should not be such a extensive operation. Of course we must not let our antivirus miss everything, but sure we do not want our antivirus take over of all system resources. This will become security fortress one day and not my every day tool for doing business or doing my personal tasks. I don't know anyone else who would like to see opposite situation.
We do not use our computers because of antiviruses or firewalls, that should be clear to anyone... we use our computers for more productive tasks, whether those are simple playing games (well those things are some people's job as well, nothing weird in that), or creating graphics, programming, selling stuff using your computer or even controlling satellites...
Unfortunately we are bombed with all those nasties (malicious stuff of all kind) on the internet, so we have to use antiviruses and firewalls. So, to me it looks more like necessity...