Have kept over 50 snakes and countless lizards and turts since I have been keeping and in that time I have never used F10.
Never had to have a vet visit or any problems since keeping.
Ask a few old time keepers how they feel about sterile setups
Im certainly not doubting your experience mate but things change as they progress and im sure you would agree that since you started keeping reps the hobby has changed alot and is now more common and mainstream.
With progress comes new ideas and techniques,but on the downside comes higher and more resilient strains of bugs and parasites hence the use of F10.
I personally agree with you to some degree that housing a reptile in a sterile environment isnt a good thing, however a monthly washdown of enclosures with such a product can really do no or little harm.
As generation after generation of reps are bred in captivity it would have to deplete the animals immunity to some degree,no?
I guess i could say im of the new school of keepers as i house my animals in glass for its display properties,and i also choose not to use a thermostat.But in saying that im not saying my way is right and yours is wrong or vice versa,im simply saying its progress.
I regularly read on the pages here that glass enclosures are bad for retaining heat and yes thats a given,melamine is much better in that example but glass has advantages in different areas over melamine also.
I guess all im saying is that we all have our own ways and have developed our own techniques whether they are right or wrong and that is what makes keeping reptiles so addictive because you never know what is down the track and will pop up in a reptile shop or trade show in the future.