I've never tried installing Debian to an external hard drive, and I haven't tried KDE in Debian, but...
Not sure what happened when you say the installer "croaked." I haven't had anything like that happen with any of my Debian installations. That goes back to "Etch" (4.0), and includes three Debian 6 installations (one was GNOME, from a CD, the other two were Xfce from Unetbootin flash drives).
I also have had no problems (yet) with Debian's grub overwriting the MBR.
I'll agree that there are easier ways to get a Debian system installed than by going with "straight" Debian. But the first time I tried installing Debian, I thought to myself, "This was easier than I expected it would be... I wish I hadn't waited so long to try it!"
If I want a quick and easy installation, I choose another distro. But when I have a little more time, I install Debian. It hasn't been all that painful. I estimate that it takes about twice as long as installing something like Ubuntu, plus additional time for setting things up to my tastes.
I don't believe Debian is meant for the desktop computer user, not vanilla Debian. It is well suited for servers, but for your everyday desktop computer user, and especially for those new to Linux--Debian is probably not for you.
I've been happily using Debian on the desktop for over 5 years now. Not sure how many fresh installations I've done, but I'm guessing something like 7 or 8. "Straight" Debian might not be the best option for those new to Linux, but after I'd done a few other Linux installations, it wasn't too difficult for me to get Debian installed and running. I don't see any reason why Debian should not be "meant for the desktop computer user." But I guess it depends on the user.
I've chosen to do fresh installations rather than upgrade to the next release each time. Just the way I like to do it. But for each release I've tried so far, the extra time it takes to install (compared to other distros) has been well worth it. Each time, I know I'm getting two or more years of problem-free, worry-free desktop use.
Anyway... just offering another point of view...