I think all research gets this to some extent. I learnt to leave a 'comments' section at the end of my online surveys so I didn't get irritating emails like "your questions are repetitive" to which I had to just say something like "that is because I am using a questionnaire that has been used for 20 years in my field, it answers a range of similar questions to make sure it is measuring the information correctly" blah blah blah.
My subject is quite emotive as well so I had comments like "when are YOU going to do something about this issue??"
It is stressful, but do try to remain professional at all times - don't send off any 'silly' replies and keep any emails in a separate file in case you get any issues with ethics etc - you only need one person to complain to cause you a lot of stress.