No, it's not okay to trash ANY host for any reason. It's rude and insensitive. How would any of you like it if someone commented in a public place about your job performance? Or your looks? Or if you aren't employed, they commented publicly about you anywhere for any reason? If you don't care for a particular host fine, simply don't watch that host.
No one cares about what any of us think about any host. If a host is successful, i.e. products that host presents are purchased, he or she continues, if not the host will not be on long.
I could care less who's hosting. If I like a product, I consider purchasing it and sometimes do; if not I don't purchase it.