Default blocks are difficult, one of the things the dev of the Tesseract frontend got absolutely roasted for a few months ago was for how aggressive the block list was and blocking Blähaj just reeks of transphobia. (The primary issue was his lack of disclosure of the existence of the block list.) There is no low controversy way of making a default block list beyond what we already do with most instances defederating a couple of the most egregious instances.