In fact thousands of people's computers all over the world download the chain every 10 minutes and automatically verify what you've said.
So suspicious activity like reorganizations are spotted instantly.
What you read is the 51% attack. There used to be doublespends attacks back in the good old days of huge pools, against a dice roll gambling site. You can look it up, the site has a bug , that enabled the attack.
But currently there is no evidence that there's doublespends going on today, (except against 0-confirmation sites) so feel free to report or mention any suspicion that you may have.
0-conf sites don't really count as an attacks because everyone knows that accepting 0-conf transactions is unsafe.
EDIT: you see the problem with 51% isn't that it won't be spotted (it will), but what can be done about it.
Making Bitcoin centralized would "solve" the problem users have:
- payments do not confirm
- The attacker makes received funds return back to senders for fun
- coins value drops to $0.01 ... actually the price will start tanking much sooner when rumors that 51% attack is about to happen
This is false. Even with 51% attack (or 99% attack or 100% attack) The real owner still controls their funds. But the attacker can return the funds back in time to previous owners or create fake histories. But the attacker cannot steal for example coinbase transactions, so users in principe could "put" their funds to miner's wallet to save the funds from going back to whoever sent them.
Another possible solution
The honest users can all go to factories and make more mining devices. In this way, the honest users could regain control of the network and "save" Bitcoin.
But don't worry. Dogecoin will work correctly.