I heard that the expansion makes Gothic 2 a lot harder and I don't want to have a harder time than I have to so I want to play without the expansion.
Problem is, there doesn't seem to be an obvious way to do this and google is no help at all in answering this question, so I turn to you, GoG forum-goers!
Can I remove the expansion? Or am I stuck with a game I'll never play?
Thank you for your time.

You're a champion!

You're Welcome.
Have Fun ;)

Be aware that you're loosing A LOT of additional content by uninstalling the add-on though. Jarkhednar is great to explore.
You might wanna try the basic Gothic 2 on your 1-st playthrough, but be sure to give full version a chance on your second playthrough.

I'm really glad that I removed the expansion now. I've never cursed so much at a video game in my life and if it was any harder, I think I'd pop a blood vessel.
It's pretty fun though, fun enough to make the difficulty and controls bearable. It's been a while since I've played a game that makes me late for work because I thought I'd only played it for 10 minutes, when in fact I'd been playing it for an hour and a half!

Has the option to install without the add on been removed? I don't see it in the installer anymore.

The new installer doesn't have this option for some reason.

See this post for a workaround:
https://secure.gog.com/forum/gothic_series/forced_to_install_notr_in_g2/post17

I have the retail CD *and* Steam version of Gothic Gold, and I actually bought the GOG version long ago because I found out through a friend that you could opt not to install NOTR. I never hated an expansion more than that game. After having gone through Gothic 2 a whopping five times, I was ticked off that NOTR ruined the balance. Cheated my first time through NOTR, than *BARELY* beat it using A.I. exploits and visible range glitches. So utterly frustrating.

Vanilla Gothic 2 is still far better, and you really aren't missing any story crucial content.