I've seen them actually used within a medical and social services setting due to my job so yes they're very much needed and exceedingly beneficial for people with a variety of conditions that may not be externally noticeable. However, the reason for the current hate on them is assholes using loose legal terminology of support animals to bring pets on to flights or claim their dog is one even though it was never trained as one. Again though this abuse is projected on to the greater realm of support animals due to the reactionary nature of media and the US culture in general.