With all due respect, land mines are not a "stupid" weapon at all 1. Used properly, they are a very effective, very cheap and very safe method of defense -- unless you're the enemy, that is.

Consider the real-life example of Finland, a sparsely-populated country with a very long land border with Russia. Finland and Russia have had more than their fair share of tussles over the centuries, so most Finnish military doctrine is concerned with the (highly non-trivial) problem of keeping the Russkies at bay.

Now, guarding a thousand-kilometer-long border against an invasion is not an easy task. Having learned the hard way that nobody else really gives a rat's ass about the place, Finland cannot rely on and hence does not belong to any military alliances. Finland does not have the luxury of a nuclear deterrent or superior armed forces. Posting guards at 100-meter intervals for the entire length of the border would tie up the entire Finnish army, not that a single guard could even do very much when that column of T-72 MBTs comes rumbling down. Finland's air force is no match for the Russian one, so destroying the tanks from the air (as the US did during the Gulf War) is not an option. There is precisely one effective solution: land mines.

A mine large enough to disable a tank doesn't cost much and it will (notoriously) stay primed and ready for decades. It's not necessary to mine the entire border, as the enemy (hopefully?) does not know which places have been mined and thus crossing the border at any point becomes more risky. Clearing a path is a slow and painstaking job, slow enough to allow reinforcements to be brought in. In all, mines increase the cost of an invasion and make its success less likely, reducing the likelihood of war. To put it another way, mines save lives.

But what about all those poor innocent children stepping on mines by accident and getting their limbs blown off, I hear you ask? Sure, this happens in places like Cambodia, where mines are used indiscriminately or on purpose as a tactic of terror. It does not, and will not, happen in places like Finland. Consider:

  1. The Finnish army is not afraid of Russian guerrillas on foot, it's afraid of tanks and for them it needs anti-tank mines. These requires hundreds of kilograms of pressure to detonate, and a person could safely dance the balalaika on one.
  2. Mines are dangerous only if you don't know where they are. This is why the Finnish army, like all modern militaries, maintains careful maps indicating exactly where every single mine is. Most anti-tank mines can even be detonated by remote control, making the task of mine clearance effortless.
  3. And the biggest reason civilians will not be killed by Finnish mines is that, as far as I know, there are no Finnish mines deployed anywhere at the moment. It is enough that the army has sufficient stockpiles and detailed plans for laying them in, say, 24 hours if things start to heat up.
There are plenty of countries that use mines extensively and responsibly, e.g. Israel, the United States (post-Vietnam), China, even Russia (although some Chechens might disagree with me on that). The problem is the countries that use them irresponsibly, and do you think the Khmer Rouge, the Taliban or the Lord's Resistance Army give a fig about some high-falutin' UN treaty? Mines are trivially easy to assemble on your own, and the types with the highest civilian body counts are usually domestically produced. Wishy-washy feel-good "mines are bhaaaaaaaad" campaigns will do nothing to stop the slaughter, and the same effort would be much better expended in either investing in mine cleanup efforts or, better yet, attempting to convince the guilty parties directly of the error of their ways.

1) Except in the sense of not being so-called "smart weapons", the latest buzzword for horrendously expensive guided weaponry aimed at specific targets. But I think both blubelle and I are referring to an overall strategic perspective here.