I’m not really arguing against your point, just pointing out that your statement isn’t necessarily true. You said that if you do any network or disk access then validation will be negligible as it would be dominated by that. I’m simply saying that while this is probably true in most real world cases, it may not be so if for example both validation and normal request handling do a simple database query, then validation is 50% of the request time (or 25% if the request takes twice as long etc). Since the person you were relying to above said something about performance sensitivity, this overhead could be too much.

Having said that, I do believe that what you’re saying is the right approach for 99.9% of use cases and I would imagine that in almost all cases the performance hit really is negligible.