clamav in PureOS is a fork to not suggest a package which in Debian contains nonfree code (see T76).
PureOS however do not ship nonfree packages, and the suggestion is therefore - in the context of PureOS - not promotion of nonfree software but merely "promotion" of non-existing (and therefore undefined regarding freedoms) software.
Please reset to again track the Debian-shipped clamav package.
Originally these choices were made because we were asked to remove the references on the FSF mailinglist to get PureOS endorsed. They also asked us to remove the "non-free" component reference from the APT manual pages.
However, nobody seems to insist on that anymore, and your reasoning makes sense to me, so I will gladly resynchronize this package with Debian.
2018-11-14 15:16:46 - INFO: Imported 'clamav_0.100.2+dfsg-1.dsc' to 'landing/main'. 2018-11-14 15:17:42 - INFO: Imported 'clamav-base_0.100.2+dfsg-1_all.deb clamav-docs_0.100.2+dfsg-1_all.deb clamav-testfiles_0.100.2+dfsg-1_all.deb' to 'landing/main'. 2018-11-14 15:17:44 - INFO: Imported 'clamav-base_0.100.2+dfsg-1_all.deb clamav-freshclam_0.100.2+dfsg-1_amd64.deb clamav-milter_0.100.2+dfsg-1_amd64.deb clamdscan_0.100.2+dfsg-1_amd64.deb clamav-testfiles_0.100.2+dfsg-1_all.deb clamav-daemon_0.100.2+dfsg-1_amd64.deb clamav_0.100.2+dfsg-1_amd64.deb clamav-docs_0.100.2+dfsg-1_all.deb libclamav-dev_0.100.2+dfsg-1_amd64.deb libclamav7_0.100.2+dfsg-1_amd64.deb' to 'landing/main'. 2018-11-14 15:17:47 - INFO: Imported 'clamav-base_0.100.2+dfsg-1_all.deb clamdscan_0.100.2+dfsg-1_arm64.deb clamav-daemon_0.100.2+dfsg-1_arm64.deb clamav-freshclam_0.100.2+dfsg-1_arm64.deb libclamav-dev_0.100.2+dfsg-1_arm64.deb clamav-milter_0.100.2+dfsg-1_arm64.deb clamav-testfiles_0.100.2+dfsg-1_all.deb clamav_0.100.2+dfsg-1_arm64.deb clamav-docs_0.100.2+dfsg-1_all.deb libclamav7_0.100.2+dfsg-1_arm64.deb' to 'landing/main'.