Seriously. WTF is up with that?
One of the nastier aspects of [del:1187h8r9]Lord Voldemort[/del:1187h8r9] You-Know-Who was that he wanted to rule over both the wizards and Muggles. But surely he can't be the first, and surely the others can't have all failed.
Consider: the best reason I can see for the entire wizarding community to keep their existence concealed, when it would be much easier for them to be able to use magic whenever they felt like it, was if there was a balance of power - if they were afraid the Muggles would rise up and kill them or something. But no such balance exists - wizards would totally pwn Muggles. Even if they were restricted to using just memory modification, stupefy and steel-capped boots the war would be difficult. Throw in an Unplottable missile silo or something and you are there.
Now, I know an explanation has been offered for this - the Muggles would demand magical solutions to all their problems if they knew about the wizards. But so what? Wizards would not be friends with Muggles, they would rule over them as superior beings. Maybe not at first, but unless science works out how to duplicate or counter magic, wizards would be the ruling elite of the whole world within a generation.
Is that what they are trying to prevent - the inevitable creation of 2 classes, those who are magic-capable and those who are not? Is so, the altruism of both the Ministry of Magic and the wizarding communities at large should be commended.
Of course, an intermingling of cultures would help the wizards too. If 2 wizards are to duel, each with a wand, the stronger wizard will win, unless some weird thing happens like the wands start having angry sex and Harry can see his parents again. But not if the weaker wizard has a sniper waiting in ambush. There are probably bullet-repelling charms, but do they always work under all circumstances? Could the rival wizard weaken the charm, perhaps?
If guns can kill wizards, they need our technology. If they can't, then that just strengthens the case of magical superiority.