The government has the monopoly on violence. It always has access to the data held by private parties. The government and the people serving it may choose to respect laws and other promises. They may choose to avoid accessing private data without a valid reason. But if the government chooses otherwise and requires private businesses to hand over their data, the businesses will most likely comply. If you don't want to give a government-turned-bad access to some data, that data must not be allowed to exist in the first place.
Given that it's already out there, there's not much more to fear in terms of a slippery slope. All that's left is to at least force the public sector to disclose more of what's going on and regulate how private interests are allowed to use it.
Otherwise, we already have the dystopia you're imagining, we just don't see it as well.