[fetchmail]What's bad with qmailinject?

Hello,
        I use for my mail handling mutt and qmail, as you can see from the 
header and also fetchmail. I was very supprised by the new feature of 
fetchmail, refuse service with QMAILINJECT enviroment variable set (and 
commented it out in the fetchmail source code immediately).
        Could somebody explain to me briefly what's this feature good for, or 
what's bad with the mails delivered with it (e.g. this one)? If there is a good 
reason, I'll stop use it. Thank you in advance.

Sincerely confused

Karel