It's not. I've been using Debian GNU/Linux as my main OS for well over a decade, and I love it both on technical merits, and on the great effort put into it to maintain a user-driven, non-profit, democratic (both in the sense of voting, but even more in the sense of participating) organization.
All that said, I've used Ubuntu on and off since it launched, and they've been a great benefit to both Debian and Linux in general. There were some issues in the start, with not handling cooperating and resource sharing very well, there were a few sore people as a result of that -- but as far as I can tell most of those growing pains are well behind us now.
I personally sneer a bit reflexively when people mention Ubuntu on the server, but frankly that's an issue with me, and not with Ubuntu. I got burned by Ubuntu doing stuff like changing gid/uid numbers for system groups/users and little incompatibilities that made it hard to maintain services across Debian old-stable, stable and a couple of Ubuntu LTS releases at the same time for a while (the typical incompatibilities which generally have plagued Linux for as long as there have been more than one distro).
My impression is that since Ubuntu 12.04 pretty much all the major kinks got worked out, including avoiding issues with LTS -> LTS release upgrades - and Ubuntu is now as solid an OS as pretty much anything else.
As for the security bit, I think Ubuntu still comes with more out of the box, both on the server and on the desktop than Debian does. Like eg. the ssh daemon, maybe some bonjour networking stuff. Ever since OpenBSD forced everyone to re-examine what "runs by default" I prefer a cleanly installed OS to not listen to neither UDP or TCP at all out of the box. In that sense, Debian might possibly be considered "more secure" -- but I don't have the impression that there's a big difference in patch rates etc between the two.
Ubuntu/Canonical has gone to great lengths to make Ubuntu for Desktop and Server work out-of-the-box for the great majority of users -- and I honestly think they've done a great job with it. I still prefer Debian, but I also accept that it's a matter of preference not some strict criteria of superiority or the like.
All that said, I've used Ubuntu on and off since it launched, and they've been a great benefit to both Debian and Linux in general. There were some issues in the start, with not handling cooperating and resource sharing very well, there were a few sore people as a result of that -- but as far as I can tell most of those growing pains are well behind us now.
I personally sneer a bit reflexively when people mention Ubuntu on the server, but frankly that's an issue with me, and not with Ubuntu. I got burned by Ubuntu doing stuff like changing gid/uid numbers for system groups/users and little incompatibilities that made it hard to maintain services across Debian old-stable, stable and a couple of Ubuntu LTS releases at the same time for a while (the typical incompatibilities which generally have plagued Linux for as long as there have been more than one distro).
My impression is that since Ubuntu 12.04 pretty much all the major kinks got worked out, including avoiding issues with LTS -> LTS release upgrades - and Ubuntu is now as solid an OS as pretty much anything else.
As for the security bit, I think Ubuntu still comes with more out of the box, both on the server and on the desktop than Debian does. Like eg. the ssh daemon, maybe some bonjour networking stuff. Ever since OpenBSD forced everyone to re-examine what "runs by default" I prefer a cleanly installed OS to not listen to neither UDP or TCP at all out of the box. In that sense, Debian might possibly be considered "more secure" -- but I don't have the impression that there's a big difference in patch rates etc between the two.
Ubuntu/Canonical has gone to great lengths to make Ubuntu for Desktop and Server work out-of-the-box for the great majority of users -- and I honestly think they've done a great job with it. I still prefer Debian, but I also accept that it's a matter of preference not some strict criteria of superiority or the like.
Oh, and I have a special place in my heart for Debian/kFreeBSD even if I've yet to actually get to play with it: https://wiki.debian.org/Debian_GNU/kFreeBSD
Phew. Apologies for the long post - hopefully it has a few interesting nuggets.