The bulk of my below post is summarised from elsewhere but I think holds true to some of the discussions here.
People use the same words - "clash" and "contrast" to mean different things. It's like when we say ‘a red car’. You have to be specific to avoid confusion between say, a fire-engine red vs a burgundy or maroon colour.
People will say “Souths clashed with Brisbane last night" and they are (correctly) told they're wrong, because visually it's true, they don’t clash. What they should say is that “Souths don’t contrast with Brisbane”, which is entirely correct, and can form the basis of a correct argument in support of alternate or 'clash' jerseys.
Basically the term "clash jersey" is biased. It implies we don't need jerseys to contract, just not to clash. The purpose of clash jerseys should be to maximise contrast rather than reduce clash.
We need to recognize that use of the word ‘clash’ implies there is no need for a contrast. The merit of whether we need totally contrasting jumper match-ups is another topic, but I think adding the term contrast to our debates here would be helpful.