It was identified as being vulnerable to cache poisoning a few years ago:
http://seclists.org/oss-sec/2014/q4/592
And this was a few years after publication of RFC5452 (2009).
Many Linux people simply have their heads in the sand with regards to systemd and it's pretty much "bandwagon fallacy" all over again, where systemd fans are sneering at anyone who doesn't want systemd and treating the widespread adoption of shit code as "inevitable". This really proves that systemd fans aren't so different from the average windows user, who many in turn look down upon.
It seems to me that some are so heavily invested in this crap that they can't easily back out and just want others to just shut up and put up and do the same, so that they can feel more at ease with their choice.
The old "you don't have to use this bit or that bit" excuses from the apologists are wearing a bit thin.