Agree with the last thing 100%. I stop AVAST from doing anything automatically except update the definitions.
Adding every .zip or .rar archive you download to the exclusion list would be just too much hassle. It is really impractical to suggest that, particularly with AVAST's clunky global exclusion list system.
What is needed, if it has still not been done yet with the latest versions, is to give the user the choice to add it to the exclusions list at the end of the on demand scan. That means the excluded file itself and not just the path because in the case of a download that will almost certainly be changed.
I've often come across zip/RAR files I've just downloaded which AVAST has not blocked or flagged any warning but on demand scans report as a problem. Compressed file formats may be flagged simply because they "could not be scanned' and some highly compressed archives are reported as possible zip bombs too.
Yet if I ignore those warnings ie. because I've elected to do nothing thankfully AVAST will still 'allow' me to move and unpack them without issue. But surely what this indicates is that the resident shields and the on demand scans are effectively at odds. The resident shields are allowing something on to your PC, for it to be copied or moved and unpacked which on demand scan of that same file will be reported as a problem.
Even if you don't want AVAST interfering in your choice to do that, and I certainly do not, doesn't that suggest there is still a good reason for using on demand scans for any download most of which will be zipped or RARed archives?