Well let's have a go then.
#5 - I'd say that not paying Alys for help would be 5th maybe? I mean, if Hahn didn't pay for those 2 to go with him he'd probably never get to Zema.
#4 - Sandworms maybe? Or at least for people trying to rear them on a certain ranch. Not exactly a good idea.
#3 - Strange abandoned caves housing ancient facilities like the Bio Lab. Let's face it, any place that remains active after that much time is probably somewhere you don't want to go. Especially if it's hidden under a mountain. There's usually a good reason for it.
#2 - People like Zio. Boy as soon as someone like him starts making trouble you'll be going from one end of the world to the other to undo the mess he's made, killing tons of monsters along the way and taking in the above mentioned dangers.
Then it's all the way back to the other end of the world again repeating the process before storming Zio's magical, mystical fort of weirdness, kicking his army to the kerb along the way before finally have a showdown with Zio and kicking his butt good and proper for all the aggravation he's caused.
#1 - Crash landing spaceships. While it may be cool to some, if you end up landing on someone's temple in the process you then have to explain yourself to some olde eccentric priest before being landed with the prospect of him tagging along with you and telling his weird jokes and making the occasional quip, all just to overlook the destruction of the temple. Especially considering that, given he's old as he is, you could just run out of said temple and bypass the whole process, as he won't be able to catch up with you.
