- allows for easier money laundering
- provides easier ways to fund terrorism
- allows for ransomware creators (like cryptolocker) to anoymously accept ransom payments for their ransomware/malware
- allows for easy and high value theft (here is another great look at high value btc theft)
- can easily be lost if your digital wallet isn't backed up, like a 9 million USD loss
- is not protected or here is another great look at high value btc theft
- while not inflation proof currently extremely volatile
- may cross all borders but in Russia they've been banned, several other countries looking at legislation, China has told it's banks DO NOT TOUCH essentially
- if it starts to catch on muggers will approach you "transfer your btc to this wallet!!!" they then press a button on their custom app and it starts bouncing around dozens of wallets effectively becoming unrecoverable even if they are apprehended by authorities.
- actually not a very fast way to transfer money, can take 9 to 19 minutes or more to move from one wallet to another, man I'd hate to wait in a drive-thru line for that
- not everyone accepts it for payment, most likely never will and the number of institutions allowing you to to exchange for physical currencies are few and shrinking in number due to legislation in parent countries as well as hacking & DDOS attacks.
- has given birth to a whole new form of malware that infects systems for the sole purpose of turning them into mining zombies for distributed mining
- would require lots of new regulations before you could use it to invest with, to avoid money laundering and insider trading
- once all 21 million BTC have been made, if it were to catch on and be a dominating currency prices on things would be terribly inconvenient, a Chevrolet Impala might be 1BTC while McDonalds would have a 0.00004347826 BTC menu (assuming the car was 23k USD)...
To expand on that last point... it would actually be far more horrible on the fractions, currently 7bn people alive, potential for a total of 21m BTC...that would be 0.003BTC for each person, if the population were 8.5BN by then... 0.00233333333BTC per person alive. Whereas there was approximately $1.25 trillion in circulation as of February 19, 2014, of which $1.2 trillion was in Federal Reserve notes which would be 178.571428571 USD per person currently alive... but only a fraction of the world trades on the dollar. Chiefly just the United States, so 350m or so people. A lot of the arguments for BTC 'oh it's a global currency everyone can use' yeah, if everyone wants to become experts at decimal places to the tenmillionths or beyond.
I don't know about you, but I'd rather say make 10$ an hour than make 0.0004347826BTC an hour. People aren't going to want to mess with insane decimal places.
