True, for absolute fixed strings, the author's approach is superior.

Off the cuff, another way to do it is with awk's index function. I don't know what speed penalty this might impose.

  $ cat ~/fmgrep
  #!/bin/awk -f

  BEGIN { split(ARGV[1], s, ","); ARGV[1]="" }

  { m = 1; for(c in s) if(index($0, s[c])) m = 0; if(m) print }

  $ ~/fmgrep sshd,systemd,polkitd /var/log/secure