For example, if I want to buy something online, I have to buy with this Bitcoin.
All you need to do is have a debit/credit card. This is more than enough for online payment.
Bitcoin wallet protects the confidentiality of transactions.
I think only Monero can provide sufficient privacy
For example, in the case of Bitcoin, there is no fear of being swindled.
There are things like Double spending and 51% Attack. Try to read about them at your leisure.
Of course, Bitcoin is the future, but it is not as infallible as some imagine.