It's nonsense. Until studies show that excess protein causes these issues, there are many other concerns to worry about. This is especially for someone who is very active and continually tearing down muscle tissue. I've been doing 200-350 grams of protein (male, 5'8, 175 and trying to gain even more) for a 10-week cycle and still going. Haven't noticed any acute issues. I've also been supplementing with other things and heavily with Creatine. For massive whole food protein meals, I've supplemented with HCL, even though it's not needed for a typical meal or on a regular basis (not on the high protein). It helps, tremendously.
I've noticed no digestive issues. Normal bowel movements, 2-3 times a day and actually, very routine and comfortable. I've also made sure to stay very hydrated. This is key, both with the Creatine and the excess protein. I do think someone who doesn't stay hydrated may have issues with digestion and cognition. However, I think something as simple as increased fluid intake can mitigate a lot of the overload.
One thing to caution, at least anecdotal. I don't think it's absolutely optimal or ideal to go on a lifetime of excess food intake. Not necessarily protein, but just constant eating and supplementation. It's best done in cycles and again, mitigated by making sure the food quality is as good as possible. If that is done, I see no reason why it can't provide very good results and not cause any health problems.