Diana was hardly the first to morally condemn the use of land mines in war (even I beat her by about 17 years, and I'm certainly no moral paragon!).
There are "rules" to war. Some make sense, many don't. None are well-followed, even the bans on chemical weapons. My .22 and 12GA shotgun, for example, would be technically banned by the Geneva conventions (which once attempted to ban airguns) whereas white phosphorus bombs and napalm are not. Many in the governments which have used these far-more devastating weapons would like to ban my ownership of these weapons (which I have never used against a human). "Cold, dead fingers."
The rules (almost NEVER followed by any government) for mines involve marking the minefields clearly and mapping the locations of mines well enough so that they can be removed after conflict. This doesn't happen. Indeed, with some weapons, such as cluster bombs, there are deliberately unexploded "mines" spread all over by mere use of the weapon. These will go off like a grenade at the slightest movement, yet "first world" governments use them whenever they want to, with no moral condemnation (at least none that I've heard) from the anti-mine people, who generally focus on buried mines. Ignoring war-rules conventions seems to be an art-form among the politically well-connected.
There is no effort I know of to target mine-making companies for economic boycotts, and any rule that is not agreed to by ALL nations would be unilateral disarmament. I am not a fan of the philosophy of unilateral disarmament for individuals, and it's been shown not to discourage fascists in the case of governments.
I have considerable intellectual support in this view:
I do believe that where there is a choice only between cowardice and violence, I would advise violence. -- Mahatma Gandhi
I doubt that he meant a fistfight. He also said:
Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest." -- Mahatma Ghandi
"Gandhi, An Autobiography", M. K. Gandhi, page 446
I (of course) would not force individuals to feel as scared as I do of government, or to arm themselves. I only ask that I be left in peace, with freedom to express my "extremist" views and own my "dangerous" weapons.
The bottom line, which I'm sorry not to have gotten to sooner, is that until nations obey the present rules about laying mines I doubt that making yet-another will have any real-world effect. If one wants to do some moral chest-beating, one can just as easily condemn present rule-violations (or the idiocy/inconsistency of present rules of war "outlawing" my damned shotgun!) as pass yet another rule-to-be-ignored on mines. More attention to following (rather than making) rules seems to be in order, but if past rule- adherence is any indicator, the old saw: "all's fair in love and war" seems to fit the situation pretty well. Signatures on scraps of paper have a poor record of holding those in power accountable.