There has long been a discussion over whether humane weapons are even feasible. In other words, is it possible to create weapons that somehow protect perpetrators or lessen the damage to victims? In this context, the word humane is not an absolute but a relative concept, referring to a weapon that is less horrific than other weapons.
I am sure that the right structure is this, There has been a long discussion, aren't I?
Drones: a humane approach to war? Or a special form of inhumanity?
"There has been a long discussion" = A discussion started at a particular time and that same discussion, probably involving the same people, went on for a long time. I would expect that period of time to be something in the region of hours although I suppose peace talks can carry on for a day or so without a break.
"There has long been a discussion" = The subject in question has been being discussed by many people over a long period of time, probably many years or decades.
I had a long discussion with a friend last night about healthcare.
The government has long been discussing the possibility of taking away free healthcare in this country.
There has long been discussion over whether free healthcare is a right or a privilege.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.