The first comes from the origin of the currency. Imagine that extraterrestrials come to Earth and offer us their currency, called Latinum, in exchange for Earthly goods. Latinum itself has no use on Earth, but we are told that it is very valuable. As aliens assure us that the supply of Latinum is limited in the whole Universe, Earthlings start furiously buying Latinum, spending their own labor and treasure in exchange for it. Once the entire Earth is priced in Latinum, it appears that aliens invented the whole thing, and Latinum is a plentiful waste product of their refineries. But it's too late - aliens own so much Latinum that they can buy the whole Earth - and they proceed to do just that.
You can ask what this story has to do with the Bitcoin. Everything, it appears. Initial mining of bitcoins, done by inventors and earliest developers, was extremely simple. A guy could click a button on his computer, go to sleep, wake up next morning and be 10,000 bitcoins richer, so easy they were to generate back then. So the early developers wasted no time and minted as many BTCs as they could. The exact numbers are huge; they are still recorded in the blockchain. One could say that about 25% to 30% of all BTCs belong to that initial period, when Bitcoin was not known. Now those guys are sitting on millions of BTCs. They want to exchange them for goods, but in order to do that they need to find enough fools who will give them their goods for BTCs. That's why they worked so hard to inflate the bubble. Still they couldn't cash out because the market never became large enough.
The second point comes from technical flaws of Bitcoin. Indeed it does not require a bank or an authority who can vouch for a coin. But the other side of this is that it's YOU who is required to do all the checking. YOU become responsible for the software that runs on your computers, and for the network that delivers data to them. It's YOU who has to watch like a hawk that your computer is not hacked - and that's nearly impossible to do in a business. VISA and other c/c companies have no such problem because the validation of the money is done by them, at their processing centers, not at the retailer. But BTC is verified at the retailer. As you can imagine, a computer can be easily fooled into believing that the transaction is accepted when, in fact, it was never even done. A computer tells you only what it's programmed to do, and it's trivial to change a program.
Security is not the only problem. The distributed nature of the network requires very long times for a confirmation. You pay, and in 15 to 30 minutes the cashier tells you that your payment has cleared and you are free to go. All those willing to wait so much at every store, raise your smartphone!
Yet another issue lies in the fact that BTC payments are not free. Some may be free today - but without any guarantee that they will be accepted by the network. Users are "encouraged" to pay some small fee to cover expenses of miners (who sign transactions.) However that "small fee" is not that small, and in the end it may amount to tens of cents per payment. It's a new tax on all economic activity! This does not compare favorably to a credit card which pays you for the purchase. Payment in cash, or in BTC, only means that you pay 5% extra to the merchant.
Yet another issue relates to the mining companies. They are in business only while there is money to be made. But miners are essential parts of the network; without miners you cannot conduct transactions. Bitcoin fathers believe that miners will be paid with transfer fees after the bitcoins cannot be mined anymore. There is no justification of such a belief. If the fees are small, they won't cover even the power bill. If the fees are large, BTC will die on its own.
There are many other issues with BTC, such as lack of traceability. Each and every payment is final and irrevocable. But it's not productive to enumerate further. The Bitcoin is an interesting technological and social experiment, and perhaps some future digital cash will be based on it. But in order for such money to become accepted, it should be far better designed and introduced. We do not want to adopt new bills if the workers of the printing house printed a few hundred tons of them for themselves.
However it is refined, the blockchain concept is the Skynet of currency. It WILL not go away, imho.