My guess, he sells UV systems and does not sell SWGs.
A SWG is a little expensive to install, and the cell needs to be replaced every three to five years, also somewhat expensive. On the other hand, you no longer need to purchase chlorine. Depending on the pool and the SWG, the SWG might end up costing less, but for most residential users the SWG will end up costing more. Most people feel that the convenience is worth the extra money.
It is possible for salt to corrode pool equipment, but this hardly ever happens in practice. Most people have no problems at all. Most of the remainder discover a couple of screws or bolts that were made of inferior materials. Only extremely rarely is there a dramatic problem.
Pool levels of salt in sewer water is a minor issue in a few places. Comparing it to toxic waste is ridiculous.
UV must be used in combination with a sanitizer. There is no way you can simply switch a SWG for a UV system and still be able to use the pool, without also adding chlorine (or some other approved sanitizer). Even when used with chlorine, UV systems are not particularly helpful for outdoor pools. The sun already provides large amounts of UV light to the pool.
