It's not engine damage, it's injector and injection pump failure either of which is inexpensive to repair. Witness the Bosch CP4 injection pump explosions on Chevy Duramax engines. These pumps were designed with European lubricity standards in mind. North American lubricity standards are lower. Own a common rail diesel? No lubricity improver used? Some owner down the road will experience a pump,or injectors failure sooner rather than later.
Agree to an extent. Conventional rotary injection pumps are a different animal, and are more sensitive to lubricity issues. These are used on many marine diesels including some Deeres. I ran a VW Beetle diesel, which had a Bosch rotary pump, for 10 years and religiously used a lubricity improver.
US diesel fuel lubricity does not meet many diesel engine manufacturer requirements. However, in spite of that, I am not seeing wholesale pump failures in common rail or other systems. If we were, European diesel engine and car/truck manufacturers would not sell and warrant the product in the US.
Having said all that, I am an advocate of lubricity additives like Stanadyne Perf Formula, it improves cetane as well as lubricity.