"risks of theft": cash is also at high risk of theft, yet cash works alright in the real world. So why not Bitcoin? Web wallets need to develop excellent security procedures, like banks, and the best ones have done so: MtGox, Coinbase, etc.
"risk of government legislation": so far governments have been welcoming to Bitcoin. A US Federal Judge have ruled Bitcoin is real money [1]. The US Treasury Department FinCEN said Bitcoin "hold greats promise" to the US economy [2]. The German financial regulatory agency, BaFin, has officially classified Bitcoin as a commodity. Australia said they would investigate Bitcoin thefts with the same thoroughness as cash thefts. China is tacitly approving Bitcoin as government-controlled China Central Television is increasing its coverage of Bitcoin, with a surprisingly positive tone(!) Canada is very Bitcoin-friendly (hence the first ATM located there). Etc. And keep in mind it only takes a handful of countries to be friendly to Bitcoin for it to have a safe base to rely on. It is highly unlikely that ALL the countries in the world will ALL be hostile toward Bitcoin.
"risk of the system being gamed": there are no such risk. That's the one thing about Bitcoin you can trust: the protocol is ruled by cryptography and algorithms. It has been reviewed by many security experts. There is no known way to "game" the system. Some theoretical attacks exist but are never practical (eg. require investing half a billion dollars in mining hardware!).
"risk of wild fluctuations": true. But on the long term, as trading volume increase, volatility will reduce.
[1] http://www.forbes.com/sites/kashmirhill/2013/08/07/federal-j... [2] http://www.fincen.gov/news_room/speech/pdf/20130613.pdf