Of course there is no such thing as a "good reason" to commit crime, but we all know that there have been some (if not many) cases in Detective Conan that are "famous" for the culprits' motives being too unreasonable and nonsense, even for a fictional series.
So which motive(s) in DC that you think are WORST ?
This is my Top 5:
1. Find the Buttock's Mark (Canon)
What the heck is THAT ? The first time I read this case I didn't even believe that it was the motive, thinking that there must have been something wrong with the translations. But no, there wasn't :| This one is the top on my list. And yes, this case was written by Gosho and not some random AO.
2. The Amusement Park Bungee Jumping Case (AO)
WOW ! Just wow !
3. The New York Case (Canon)
What's with Gosho and the anime staff making characters kill people because of some freaking fictional characters ??? And speaking of which, here we have another one.
4. Holmes Freak Murder Case (Canon)
I don't really remember the detailed motive since I read it a very long time ago. But I recall it having something to do with...
5. Disappearing Weapon Case (AO)
Yup, this one is probably a "classic". The only reason it's only the 5th on my list is because that "motive" was only the direct cause that prompted her into killing the victim. Their relationship had became tense because of other reasons as well. This is also not as unreasonable and full of madness as the ones above IMO.