It’s convention to capitalise acronyms . Acronyms are used as convenient abbreviations to save lots of typing. For example CASA is used in place of Civil Aviation Safety Authority, BLM for black lives matter. And so on. As regards the weird feeling specifically associated with the acronym BLM my sense is this has more to do with the discomfort some folks feel when they are confronted with the idea that people of colour or of differing self identification are not in fact treated equally in line with the founding principles that are said to define America and Americans.