Because not every editor I use will automatically turn the tab into spaces. This is especially a problem when I am editing a YAML file over SSH using vi or nano, or pico or thousands of other editors.

They stick the damn tab in, then the program that is parsing said YAML file does the wrong thing and I am confused, annoyed, and most times really pissed off because I will spend hours trying to figure out what went wrong.

YAML is stupid for configuration files.