To be honest... Just live your life happily with your tupps.
A shirt like this would just scream "look at me im so speshul" in my humble opinion. Are you doing tulpamancy only for attention? xP
but the reasons that you would want it to be a little more socially acceptable would be
1. Mainstream psychological research
2. Being able to help more people with false diagnoses of DID/other personality disorders
3. More people for which having a tulpa could potentially be lifesaving would come into the community