A very simple google search brought this up immediately:

https://docs.legis.wisconsin.gov/statutes/statutes/346/ix/59...

Other states have something similar on the books as well.

Your simple search doesn't back up your position. I can assure you, going ~1MPH below the speed limit does not run afoul of that law.

I never claimed that it did.

Addendum: the margin of error on speed radar generally tends to be in the region of 2mph. You'll need to be a good deal slower than the speed limit before a police officer is likely to consider your driving to be an impairment.

It's called unsafe driving and it's definitely ticketable.

It's very smart to have laws set up so that whether you are speeding or not, you can be pulled over for a moving traffic violation! That way, the police always have a legal pretense for a traffic stop.

Many states have laws against obstructing traffic. Most of them don't mention a specific minimum speed so enforcement is largely at the discretion of law enforcement officers. Personally I would like to see strict enforcement of those laws with tickets given out to anyone who intentionally impedes the flow of traffic.

They should use the same fine schedule as speeding.

It ought to be just as lucrative for a cop to nab someone who's unreasonably stopping at a merge as it is to nab someone who's going a few over.

Obstructing traffic is very different than “driving more slowly than the person behind you wants”. Obstructing means blocking, not making them wait 30 seconds for a good chance to go around.

If you are moving a large item that is fragile, are you allowed to go 35mph in a 45mph zone to reduce the risk of damaging the fragile item? Or is that illegal too? Or what if one of your passengers gets car sick easily?

In fact, there are some winding mountain roads in California where the speed limit is 55, but if you go that fast, you’re suicidal because there are no guard rails and very sharp turns. Occasionally, someone mildly suicidal will come up behind you. Is it illegal to drive 15mph in that 55 zone?

Safety is prioritized above speed, suggesting otherwise is unhinged and antisocial.

Impeding the flow of traffic is illegal. Most states have "if x number of vehicles are behind you, you are required to use pull offs or let vehicles pass" laws.

If a cop thinks your slow driving is dangerous they can absolutely write a citation. There are a bunch of laws that allow them to do this in most states.