Have you ever been in a military organization? If so, you'll know that a bunch of random people from around the world, speaking different languages, will be incapable of organizing themselves into an effective fighting force.

You're really going into a lot of assumptions here, buddy. First off all - it's been done numerous times already. Most people speak at least basic English, so communication definitely is not a problem. And why are you assuming they're incapable of organising themselves? There are millions of christians who are also war veterans/soldiers/reservists who would definitely answer the call.

It's incredibly imaginative to think that a substantial number of people would respond to such a call

Thousands of people flock to war zones - Ukraine, Syria, Iraq, Libya, to engage in war tourism/adventurism. It's actually incredibly delusional to actually believe there aren't thousands if not millions of people who want to sign their life up and fight for a cause they believe in.

Remember, the Pope isn't the head of all Christian sects, just the Catholics, and no one is obligated to respond to his call to arms.

Many still would.

...sooooo, yes.

While it sounds nice in theory. You only have two cheeks. If someone slaps you on the one cheek and then uppercuts you in the other cheek, would you still turn your other cheek? Yeah, probably not, you'd put your hands up.

meber that the crusades were an abuse of Christianity in support of selfish human goals

That's not how I rememer it. I remember the crusades being a response to very brutal jihad wars, raids and slavery campaigns conducted by militant muslims.