The survey is broadly advertised as available, and people are invited to participate. All of the trans people I know are well aware of its existence and we communicate it’s availability to others who may not be known. No one is compelled to participate. Because the trans community understands that to get greater acceptance, the general public needs to be informed of the truth, many enthusiastically participate. I did myself. We want to educate people. This is a very useful tool to forward the process. The detransitioned can also participate. The only screening that is done at the beginning is to ask a series of questions about what kind of a transgender person the participant is and questions about their current status and identity among other things. They are open ended questions that people are able to answer honestly to give a clear impression of who they are. The data is then gathered and reported to allow people to draw valid conclusions and understand the diverse nature of the trans community better.
The only people who would be culled from the analysis are those who are not transgender or who have never considered themselves as such. This is designed for the transgender community, not allies and transphobic and cis people who do not identify as trans. That is entirely appropriate. The purpose is solely to develop data regarding the nature of the trans community and their attitudes and status. They are the ones who have dysphoria. Other people do not. Therefore, they are not part of the community of people about whom data is being gathered.