No doubt, Bitcoin is a great retirement option. But it isn't really hassle-free. It isn't actually 100% smooth and convenient all the time as you may want to portray it. It has its own share of hassles so to speak.
Bitcoin isn't really just inside your pocket and you don't need to do anything to use it. You will probably have to convert some, so you still have to deal with the banks and other third parties. There might still be delays and other glitches.
Bitcoin is also not an anytime money. Its volatility means there are good and bad times to transact.
As to possible threats and harm, you're actually not free from them just because you use Bitcoin.
My point is that while Bitcoin indeed makes our life better, it doesn't actually make it ideal.
I think it is important to define the timeframes and the needs or financial possibilities someone expects a Bitcoin-based retirement to provide. The timeframe is extremely important. Is OP implying that they want to replace their retirement from the government 1:1 with long-term savings in Bitcoin? If yes, when is this retirement plan supposed to kick in?
While I am firm believer in the long-term success of Bitcoin, I would still not recommending putting 100% of your savings into Bitcoin. It is still a technology with strong potential to threaten the legacy financial system. There are a couple of uncertainties that might pose some threat to short-term availability and usability for Bitcoin. I think a healthy mix is the way to go.
The volatility should probably only be an issue in the short-term, but assuming that someone starts putting monthly savings into Bitcoin for a very long period of time as a preparation for a solid retirement plan, volatility is probably going to be cancelled out mostly. It doesn't really matter whether something is volatile when it follows an upwards trend in the long run.