If you think about it, there are plenty of things we use that others already have, we just know that they can be sufficiently cleaned. For instance restaurant glasses, silverware, etc., the dentist's office, where they sterilize the equipment before it goes in your mouth and all the other health services examples.

So, if it can be sterilized, it doesn't matter if the person who used it before was riddled with disease. However, that would depend on a sure fire way to sterilize it at home & being able to do it effectively. There's also the psychological "ick" factor to get past, but I can see no problem with glass or metal. I still have my reservations about silicone because the integrity of the surface is so easily damaged by scratches & punctures that can hide microbes. It just depends on how careful you are about sterilizing it & if you trust the source. So, yes I would consider it for glass & metal, but silicone would be a more considered decision.