No arguments. My father is foreign, and at the time had no preference for a Scottish team. He told me about he went to Ibrox to watch Rangers, and was racially abused by multiple Rangers fans, and the stewards did not care. He told me about how he went to the toilet, and 2 Neanderthals stood around him calling all sorts of racist names under the sun. This was his first experience of Scottish football at the hands of "the people". He then went to Celtic Park, and his experience was the complete opposite (I remember this as a kid), they welcomed him, knew he was a "newbie" and treated him with utmost respect.
As a youngster I also experienced racial abuse generally. However, let me tell you, in almost every instance (bar one), the person dishing it out was a Rangers fan.