Unfortunately it is not clear that crypto will be able to prevent this. To allow for participation from people in the legacy economy, at some point an exchange between cash and crypto must be made. This is the weak point that can be easily attacked by governments and the banking oligarchy. Additionally, if disfavored entities begin using crypto and thriving on it, the government will simply find an excuse to sieze it under money laundering or terrorism laws, or will make something else up on the spot. Look at what happened to the Liberty Dollar for an example of what can happen to alt currencies when they start to gain real traction.
Remember, all that you have to do is make alt currencies inconvenient enough to use for normal payment needs, and this will discourage people from getting involved. Lower participation deprives the alt economy of goods, services, and the ability to exchange currency for "real" cash.
That doesn't mean that crypto is totally useless, just pointing out that there is not a technical "silver bullet" solution to this problem. Technical solutions must be part of the answer, but these must be backed by political force.