Buying Bitcoin with a debit or credit card? Online purchases are considerably cheaper than using an ATM.
Op has stated many times that he only wishes to pay using cash, so this cannot work for him.
If you use Bitcoin ATM, the decentralization of Bitcoin will no longer work here. Then it will become centralized. So all in all, I would say that Bitcoin ATM will not be able to provide us with privacy.
BTM has nothing to do with BTC's decentralization, and i don't know what you mean by it will become centralized. The only disadvantage of BTM is the high fees, kyc and lurking eyes watching you when you are using the machine.