The following contains spoilers for Jurassic World: Fallen Kingdom. Consider yourself warned.
Jurassic World: Fallen Kingdom introduces a new type of dinosaur that is specifically designed for a particular purpose. Unfortunately, that purpose is a really bad idea that will never work. The Indoraptor has been genetically engineered with the idea that it can be used by the military as a trained attack animal. The raptor is a vicious killer, that much is true, so what army could possibly stand up to such a ruthless killing machine?
This idea is a holdover from the previous Jurassic World where Vincent D'Onofrio's character had similar machinations, but it was a bad idea then, and it's a bad idea now. While raptors might be technically trainable, this idea simply doesn't hold up scrutiny. If considered for more than five minutes, the entire concept falls apart. Here's why...
You Have To Feed Them
Bringing even one trained velociraptor, never mind several of them, as part of a military campaign, means they are just more mouths to feed. Soldiers aren't traditionally the most well fed in the field with quality food because transporting food in bulk is difficult. MREs are easy to pack. It would be one thing if you just needed to pack a lot of dead meat, but Jurassic World dinosaurs prefer their food alive. If your war is taking place in a location where there is a lot of wild game, you might have a chance, though you'll need to take the time to catch it. Otherwise, your army has to transport an awful lot of live goats to feed your velociraptors or feed the dinos your enemies... which has to be a human rights violation.
They're Not Bulletproof
It's pointed out in Jurassic World: Fallen Kingdom that man has often used animals in war. This is true, of course. Cavalry fighters rode horses. Hannibal crossed the Alps on elephants. But we don't really do that anymore. Why is that? Because if you want to take down a soldier on a horse there's a fairly easy way to do it. Shoot the horse. It's a bigger target. The Indoraptor is fast and violent to be sure, but it's not bulletproof. Send it into a place where an entire army with guns is standing and while it's busy ripping somebody's throat out, everybody else is going to blow it away. We see in the film that the animals are tough, but they're not invincible.
Wars Aren't Won On The Ground
Want an easier way to kill a velociraptor than with a machine gun? Try a drone. Air superiority has been the key to warfare since World War II and that doesn't appear set to change anytime soon. While boots on the ground will always be necessary, they're not where most warfare is won and lost. It will be possible to take out any number of dinosaur soldiers without ever having to engage them directly thanks to fighter jets and drones. If ground warfare against the Indoraptor actually ends up as one-sided as everybody seems to think, the opposing army will just pull back their forces to a safe distance and negate that advantage.
They Get Tired
Ultimately, velociraptors are animals, and all animals, even unstable killing machines, get tired. That's fine, however, it means that in order to be sure you'll have the appropriate number of velociraptor weapons at your disposal when you want them, you'll need a lot more of them. Now we can take everything we said about food earlier and multiply it because you're not just feeding the raptors you need, you're feeding all the raptors that you might need if those die or just need a nap at some point. Otherwise, your raptor forces will dwindle quickly. This also means you'll need a continued supply of new Indoraptors and while we know they can accelerate the growth of these new dinosaurs, what do you do with all these extra raptors until they're needed?
They'll Lose Hearts And Minds
Only part of the army's job is fighting. The other part is to win the support of the people they're fighting for. Numerous weapons have been banned for use in war because we, as an allegedly civilized society, have determined that these weapons are cruel or too difficult to control. Such would likely be the case here. An army that fought with Indoraptors by their side might not be looked at too kindly by civilians after they saw what was left of anybody they were ordered to attack. Even if an army can win a battle with these, they might lose a war.