I said armies that could afford it should do it. Perhaps not to every soldier, but to at least one in every squad. You're right, being able to see it doesn't make it any less dangerous, but it ruins the element of surprise on the tank's behalf. Look back at your use for cloaking. It can be used to hide convoys moving supplies or troops (for example). Well, what good is all of that if someone can just put on a set of thermal goggles? I'll give you a hint: it's not good at all. That's why I brought up the possibility of heat cloaking, which you either missed or didn't care to address.
Also, why wouldn't it still be able to attack while cloaked? Please elaborate on your point.
Any army able to afford thermo goggles for every soldier isn't going to fight the UK because they're already allied with them. What good is moving your supply line if the enemy knows exactly where you're coming from in the first place? How bad is your intelligence and how bad is theirs if you don't know that they know you're coming and have already prepared to ambush you? This kind of optical stealth technology is perfect for moving unexpectedly. Send one decoy convoy one way, send the convoy you actually need equipped with the cameras in a different direction. The enemy tries to ambush the decoy convoy, only to find they've been had.
Randomly flipping on your thermo goggles isn't going to thwart any plans unless your enemy is going for a killing blow or trying to move as closely to your position as possible without being sighted. Unless you know where they're coming from, a set or 10 sets of goggles isn't going to help you. Using your logic, stealth fighters are pointless because all you have to do is look up at the sky and you'll know they're there.
Yes, let's heat cloak a giant tank driving through a desert at night. That's an awesome, and completely impractical idea unless the tank was created with heat cloaking in mind. Otherwise spraying it with water and nitrogen isn't going to do very much, especially when you have the commander pop his head out of the tank to take a look. Oh noes. A floating head. It's a ghost. It has to be.
Attacking while cloaked pretty much defeats the purpose of being cloaked in the first place unless you're randomly attacking an unsuspecting enemy. Why? A giant flash, lots of smoke, and sound of an explosion kinda gives your position away. Even if they didn't see where the first shot came from, you can always look at where the shell hit and trace it back to the enemy. That's also where your dandy thermo goggles come into play. Now the enemy knows where the tank is, and now your stealth capabilities don't matter.
Yeah, if you place that one shot just right, you'll hit a canister that will explode into a truck which in turn will also explode, causing missiles to explode, leading to the deaths of all of your enemies.
No.
This isn't Hollywood. If you're going fire off a few tank rounds, you'd better have a good enough number of tanks to suppress your enemies, allowing ground forces to move in or, if the enemy camp wasn't surrounded by nothing but aa batteries, you could have called in an airstrike.
Optical camouflage would be great for moving unseen, not for attacking, unless you're able to do so from quite a ways off, in which case you probably don't need the camo in the first place unless you're hiding from aircraft, though they'd probably be equipped with thermovision unless you're fighting bandits.