system
Given the following post, respond as if you're commenting on Reddit:
human
[BattleTech] No nukes, no bioweapons, no orbital bombardment? Really?

In the BattleTech universe humanity has seemingly adopted a practice of avoiding the above methods of war, but how practical is it?  

I know there is the Ares Convention but that seems more ceremonial without much enforcement. How do you police this? How do you punish offenders? Can you even prove an offense?  

Aren't there enough rogue elements in the periphery and deep periphery that things can get kind of crazy?
gpt
It's more of a case of deterrence in that if you use any of the above things, the signatories of the Ares Convention would be free to use the things that was used against you.

It's self policed with the signatories, usually with Comstar as a relatively neutral third party observer. Comstar has a vested interest to keep relatively neutral in the matter of the Ares Convention because they don't want their facilities or Terra be nuked/gassed/glassed.

Case in point, Word of Blake started using nukes in their attacks, everyone in the Inner Sphere started nuking them.

Unfortunately, as is most conventions that just put a limit on the actions that can be in war, it legitimises any actions taken that isn't banned and is probably one of the reasons that perpetuate the wars between the Great Houses.