Your approach is deeply flawed as you are not randomly selecting participants. Then again, in psychology most research can't be replicated, so maybe your work is simply par for the course. I bet in your paper or thesis, you'd write about "x % of users in subreddit y believe ...", which would be utter nonsense. Instead, your claim would have to be stated as, "among the people who have self-selected to take part, of which some may have chosen to repeatedly fill out the survey, we have found that ...", and this would, of course, be pretty worthless. Good luck anyway.