Apparently you haven't been following this discussion very closely, or you wouldn't have to ask that. Using your logic we should still all be changing water with buckets. Methods in this hobby are constantly advancing, and sometimes old dogs like you & I need to learn to embrace them. Not because our ways are bad ways, but sometimes, just sometimes, there are more efficient ways - like using a Python.
Probiotics don't eliminate having to change water, or clean filters, or allow one to not use a proper quarantine protocol when introducing new plants/fish/etc. to our systems. What they do is help reduce organics, which is always a good thing, and for some folks might help them go 4 weeks on a filter cleaning, vs. 2 weeks. For some hobbyists that could equate to keeping fish, or not. I consider that a plus, and Frank just demonstrated that.
With regards to pathogens, even a fish that on the outside appears healthy, can become stressed from aggression, breeding, etc, and sometimes that's all it takes for a pathogen to take hold. It could even start with something as simple as a scrape on the gill cover, lip, etc. And of course many fish that carry these pathogens, are just that, carriers, that never exhibit any symptoms of what they carry. See post # 245 in this discussion - that single pathogen alone should be enough to make one at least consider the use of probiotics. Flavobacterium columnare is a real concern in this hobby, and it is becoming more common in hobbyist tanks every year. Even those who are careful, and have excellent husbandry practices.
The point being that the introduction of numerous
non-pathogenic bacteria, can result in the starving out of
any pathogenic bacteria. Again, that side of probiotics works in the background, and no one will generally ever be the wiser of what sort of hellish nightmare it might have saved one from by performing a preemptive strike on the bad bacteria that live in almost every hobbyists system. Again, I can't see how this could possibly be viewed as anything but a plus.