There is anecdotal evidence that they are good, and anecdotal evidence that they are bad. I've only experienced good (I continued running the bike for 2 years on same piston and crank).
A single, even a few, anecdotal experiences doesn't negate scientific data. Just because someone smokes a pack of a cigarettes a day for 50 years and doesn't get lung cancer doesn't mean the risk of lung cancer isn't exponentially increased.
The problem with chlorinated paraffins is that they decompose rather quickly in high heat such as you would see on cylinder walls and valve stems. When they breakdown, they form hydrogen chloride which dissolves in water to form hydrochloric acid which is very corrosive.
Take this scenario. You dump in Motorkote at their recommended 2 oz per quart treat rate which is 6.25% of the sump. Motorkote is 27% chlorinated paraffin which comes out to 1.69% of the sump at that treat rate. Depending on exactly which CP is used, the chlorine content is between 0.8-1.2% (8,000 to 12,000 ppm) of the sump capacity. To give you a comparison and prelude for what's to come, the total amount of detergents (combined from all sources) is typically between 1500-3000 ppm which is just 0.15-0.3% or 3 the amount of chlorine and 5th the amount of CP. In this form, by itself and not exposed to heat or moisture yet, isn't really corrosive. This is how supplements advertising CPs are able to get away with saying... "Does not cause corrosion..." by conveniently leaving out the very important end to that statement... "...if you don't get it hot."
You start up the engine and go for a nice 30 minute drive on the highway. The oil is at 210-230°F in the sump, 240-275°F at bearing exit, and upwards of 450°F on the cylinder walls. In the presence of high temperatures, the CP decomposes into hydrogen chloride which you can actually smell quite distinctly. Your engine produces a lot of water as a result of the combustion of hydrocarbons. Burning 1 gallon of gasoline produces 1.03 gallons of water. Most of the water exits through the exhaust as a vapor, but some of it inevitably ends up in the crankcase. The contrast in temperature between the crankcase and ambient air allows for condensation in the crankcase which settles into the oil after the engine is shut off and oil temperature falls, adding more water to the mix. The hydrogen chloride dissolves in this water and forms hydrochloric acid. Your detergents, in the form of calcium carbonate and magensium carbonate, will jump into action to neutralize the HCl as best it can, but against so much of it, it's like Beglium vs Nazi Germany in WWII. They don't stand a chance. It reacts with iron to form ferric chloride which is also very corrosive and breaks down more iron to form more ferric chloride which can also react with oxidizing catalysts at those same high temperatures to form ferrous oxychloride which hydrolyses in that same moisture to... you get the idea. It's a snowball chain reaction of hell.
With these strong acids depleting the detergents, other weaker acids begin to spread as well. Think of the oil in this case like a human respiratory system. Covid-19 (hydrochloric acid) has tied up the immune system and reduced breathing capacity significantly making it very easy for something like pneumonia (other acids) to kill rather quickly. The oil starts a process of rather rapid oxidation and decomposition, and sludge isn't far away.
Yet, you do a UOA and see no significant increase in iron wear. You figure everything is fine. However, the corrosion is running away under a barrier of iron oxides which eventually get bad enough that the surface of the metal breaks down and begins to chip off in a process known as spalling. By the time you start to notice the damage, it's too far gone.
Also, CPs aren't even that great of a friction reducer compared to what we have out there. Moly and titanium based additives are superior to CPs in this regard in much, much lower concentrations, while also providing an anti-oxidant benefit, and already in modern engine oils.