Money is a technology, that's all. A technology can be developed and maintained to serve a specific purpose. It happens that major government money systems have been managed to serve purposes such as: Temporary store of value, convenient medium of exchange, and instrument of economic policy.

Like any technology, it works or it doesn't, and people will use the one that works the best for them if they have a choice. For instance people in some countries use their local currency for daily purchases, but store their wealth in instruments that are valued in dollars, euro's, etc. Some people will break the laws of their own countries to lay their hands on those dollars or euro's.

Money is speculative inasmuch as its value is still relative to other things such as stocks, gold, and bitcoins. Holding dollars instead of gold on any given day is a speculation. In a relatively free economy, there's no such thing as opting out of speculation.

Bitcoins are unique inasmuch as they are designed to exist without any deliberate purpose being imposed on them. The only way a government can manipulate the value of bitcoins, that I can think of, is to subsidize the electricity for bitcoin mining.