Running without a thermostat ok?

Water takes time to absorb heat, it takes time to shed heat. But unless your engine is made of transparent aluminum, I doubt the coolant is teleporting itself from the water pump to the thermostat housing, which means its spending time in the engine. The flow speed generated by engines isn't enough to keep the water from absorbing significant heat energy. There's simply too much restriction to let it flow THAT fast.

Water does transmit heat about 130x slower than iron though (at room temperature and pressure), which means that if the block is at or near the boiling point of the coolant, we need a way to mitigate aeration caused by the boiling because water near the hottest spot will boil first (much like the bottom of an egg burning first).

Our water pumps are basically belt-drive superchargers moving water. They will build 'boost' just like any other impeller system, and the more restriction down-stream the more they'll build for a given energy input (other trade offs not withstanding, such as cavitation and turbulence).

So what we have is a fine balance of restriction vs flow that helps to create the pressure we want to keep the coolant in contact with the inside of the engine surfaces to keep it doing it's job. As the mass of coolant increases it's temperature (since air-cooling isn't efficient enough to get the coolant back to ambient air temp during it's ride through the radiator) the pressure built by the pump alone isn't enough, typically, so we have pressurized caps to add even more of a 'buffer'. Increasing the power of an engine will increase the amount of waste heat which manifests as hotter internal block temperatures which means we need even greater pressure (high flow water pumps) to counteract the localized boiling.

Lower temperature thermostats will only reduce the running temperature of an engine if the radiator is up to the task of shedding the heat sent to it. If it's not, then lowering the thermostat temperature can have the opposite effect: the restriction it offers will be reduced at higher temperatures since it's open more and sooner and the total pressure in the block is reduced to the point where it is POSSIBLE in SOME CASES to allow boiling to occur. When it does, a runaway situation typically happens and we get an overheating system. Typically, if a system is this marginal, it won't fall into the narrow range where a hotter thermostat actually helps with hot running, but it CAN happen.

So: running without a thermostat does exactly as the self-appointed (and some actual) engineers point out: it increases warm up times (your rings and oil will love this), eliminates the restriction needed to build pressure in the block to help mitigate local boiling (which aerates the coolant and effectively reduces the surface area of the coolant in contact with the block) and will generally screw things up. Some systems will run hotter without, some will simply run stone cold. As with most things, the reality depends on the variables.

A 195T stat'd engine can run at 180 degrees. The 195 is probably beginning to open up at 180, and there are certainly other passage ways for coolant to take through the system (heater core, anyone?) and at the small opening it's seeing at 180 it's likely helping to build some significant pressure to help quell any localized boiling.

There are very small effects that flow speed can have, mostly with boundary layer thickness and shear of the fluid, but we're likely not going to see conditions where those are the driving characteristics of the system. Temperature and pressure are going to dominate and occasionally there will be someone with issues which can be attributed to flow speed, but they're going to tend to be the exception and not the rule.

As far as Chernobyl, it had nothing to do with cooling towers. The cooling system and it's poor design (but typical of the time) didn't help, but it wasn't the cause. Wikipedia has a pretty good run down on what exactly happened.