As others have stated it depends on the merchants. I think it also depends on what it is you buy. If you purhcase a coffee for $3 I'm not sure who would go through the effort of double-spending that and then never go to that coffee shop again? Not a lot of people I'd say.
As for the OP stating we can't buy "something" quickly I can make purchases online just as fast as when I use a CC more or less. Thanks to bitpay. I don't have to sit around and wait for the confirmation to show as long as I know that it will confirm eventually.
I'd even argue that accepting CCs as a merchant in real life is more risky than accepting bitcoin purchases with 0 confirmation, no matter what the amount is.
Look on the news, you'll see a ton of people using stolen credit card details to book a room at a hotel, buy expensive jewelry, electronics, gift cards, and whatnot. Now search up how many people are willing to do the same with bitcoin doublespends? I haven't come across a single case in the 4 years i've spent with btc. Fact is that in real life, you don't have enough time to doublespend, and it's not worth it, because everything is caught on CCTV. Even casinos accept 0 conf deposits, like Bitsler and i think bitcoinvideocasino(or used to), and never had major issues with doublespends even though the guy is behind a screen.
The main concern here is fees, not doublespends. If you're buying a coffee for $3 and the fee is $3 alone, you're probably not going to buy it in bitcoin. But if you order something overseas, online, say a macbook, doing so with bitcoin is much cheaper than pp or cc.
