If and when cryptocurrency and/or bitcoin becomes the official currency of the world, do you think there will be a downside to it? If so, what do you think the negative effect will be once cryptocurrency becomes a worldwide currency?
The only downside to bitcoin is its decentralised nature thus no proper authentic regulating body over bitcoin and thus leading to its illegal use, bitcoin being so profitable has always helped millions of people in finding their jobs and earning them a good life but still due to its decentralised nature, most of the countries are in against of it as no country wants to bring terrorism in their nation but to solve this issue, centralisation of bitcoin all over the world is the last option left as then countries governments will look after all bitcoin activities.
This post is pretty close to hitting the nail on the head. The problem with cryptocurrency as a global currency is that while the anonymity can help good people from getting hassled, it also provides a favorable environment for bad actors. And when people favor safety over freedom, they will ask for governments to sponsor and regulate crypto to catch the bad actors.
And then from there, people will want consumer protections (for example, I go to a store and buy a "new" TV that turns out to be used and broken, but I paid with crypto, so non-reversible transaction).
The problem at that point is that then the government has a lot greater control and oversight over their population than they did while using fiat currency. And at that point, you end up in a dangerous place where they can cut one person off being able to spend their funds (which can be a good thing when trying to catch a criminal, but what if you just happen to be exercising free speech that happens to offend someone in government that has access to the banlist?). And then of course the inevitable argument of what if the group in control of the government decides to go on a purge, Nazi Germany style? People could be purged based on a number of different criteria. Race, religion, income.
So you wind up in a catch-22 situation. Governments are not likely to endorse cryptocurrency unless they are government-sponsored. And people who have thought things through will likely not want to endorse cryptocurrency if it is government-sponsored.