Deleting messages on block is illegal
When grinder deletes or hides messages because someone clicked block user is harboring evidence from illigal activity. If a user failed to disclose their hiv status before engaging In sex that is illegal. For that user to have the ability to just click block and have evidence erased from the victim's view sets up major grounds of lawsuits in various countries such as USA and Korea.
Craig Martin commented
Under Australian law, you do not have to disclose your positive status to a sexual partner on the proviso that you “take reasonable precautions to prevent HIV transmission”. Anyone that has morals would tell the other person