They're owned by a for-profit company, they collect data on you by default, they've already had privacy issues in the past, and they include non-free software by default. I would rather have a beginner start off with Debian or Trisquel. We shouldn't be trapping people into these distros because then they'll potentially get too comfortable and not make the switch. This is coming from someone who did start off on Ubuntu. Sure, it's more convenient, but we should be teaching people to value freedom over convenience. Even if the data collection is minimal, it's still data.