So essentially the theory is pointless.
Depends which theories (schools) you are talking about. Economics is an attempt to explain human behaviour. It shines a mirror on our behaviour and theorises why humans behave in the manner they do, and more importantly, why some rational behaviours have positive outcomes eg wealth is enhanced and why some rational behaviours have negative outcomes eg wealth is destroyed. It then goes about explaining what is the best environment for the creation of wealth, and what are scenarios we should be trying to avoid.
It just says people will do stuff, sometimes beneficial and sometimes harmful.
Yep pretty much. But more importantly it says that individuals have reasons known only to themselves for acting economically and further, in general, we act in our best interest with the available knowledge and skills we possess at the time. Of course that doesn’t ignore the fact that many people are stupid, or don’t do dumb things, that’s just life. But it’s from this acceptance that individuals act rationally that we arrive at the next step ie that others can't be sure what is in our own best interest all the time, therefore it fruitless and even destructive attempting to design economic outcomes with the best interest of the public in mind, simply because these central planners don’t know or haven’t met most of the public.
Edit to add: economics is not rocket science. If it was, i wouldn’t understand it.