FIRE not cheating. Theft is cheating. I do not see evidence that you engaged in theft. Therefore I do not see any evidence that you are cheating. Where is your argument or evidence?

nobody will get any extra money out of me

I think most FI people plan on accruing pretty big nest eggs most of which will be passed on to their family when they die. Unless you perfectly spend it down to $0, but no one does that. Furthermore, merely by having your money saved and invested, you are providing capital to businesses and consumers to borrow and further their own interests. This is unseen to the naked eye, but it is real nonetheless. Read Economics in One Lesson by Henry Hazlitt.

If I want to buy something, I will always search online for the absolute lowest (trusted) webshop price and buy it there. I will instantly spot if any shop has a high margin on a product I want and just not buy it there and look online. I haggle on CL. I hardly ever go out to anything like bars/restaurants/etc unless invited for an occasion, because I just don't like spending money on stuff I don't need.

none of this is cheating, or theft.

My point being, if everybody lived like I do, our society would pretty much collapse.

No it wouldn't.

Economy would tank,

No it wouldn't. The economy would change

millions would lose their jobs.

Some jobs would be changed, not necessarily lost.

Everybody would try to hoard money like me.

Hoarding money isn't a bad thing, it's a good thing. As I said above, savings provides capital to businesses and consumers to further their own interests. Savings is what grows the economy, and is the reason you probably typed this post on your personal laptop, and had time to philosophize, instead of toiling in subsistence agriculture.