First of all, thank you for sharing your feelings with us! :^)
As you can see, this article discusses ClamXav, an open-source-based anti-virus application. While its author encourages donations, the application can be used free of charge. Also, it does not install kernel extensions and has optional background scanning capabilities.
Any application can, of course, under some circumstances, encounter (or cause) issues. Nevertheless, I feel Clamav and ClamXav address both negative points you mention above.