The newer discourse versions have something very nice to handle this kind of thing. Look at this for instance:
So I'd say with discourse it's okay and encouraged to go wild, don't worry. Moderation tools are in place to contain trolls. The rest is just incentivizing a community as open as possible.
Also, if you want to change the topic or go off topic, do consider using the
Reply as new topic feature instead. Simply move your mouse over the post and it will appear on the right side.