Thac0 by itself probably isn't but it's rarely if ever a question of a single mechanic being the lone point of contention around how the game should be... its Thac0, it's deterministic alignment, it's the unwillingness to admit or change old stereotypes, it's preferring the old artwork while ignoring it's lack of representing the myriad of types of players who now play D&D... and, intentional or not, whether you prefer these things or not... its creating barriers to others playing the game and is a form of gatekeeping. Your intention doesn't change the effect.