I personally agree with the view presented in the OP outright, but there is another view to be taken. Even if you disagree with the premise OP is putting forward, that your behavior and skill should be separated in terms of in game punishments and rewards, there is still a suitable reason why this is a terrible choice by Riot.

That reason is reform. Riot SAYS they place a huge emphasis on player reform and have gloated in the past about the very high reform rate of players who receive shorter punishments by the automatic tribunal and that players very rarely repeat offend once they have been warned or given a short ban. If this is true, if Riot really believes their system is reforming players to better behavior and is successful... they DO NOT NEED an additional way to punish past offenders.

This decision shows a blatant disrespect for the concept of reformation at it's fundamental meaning. It is essentially saying "even if you are reformed and served the punishment deemed appropriate for your offenses, you will experience further penalties". Even if you agree that behavior should impact rewards earned through skill, there is no denying the blatant hypocrisy of gloating about player reform while continuing to punish so called reformed players. If they really want to push this extra layer of punishment on top of whatever the automatic system deems fair for your infractions, they should implement a system that only applies it to players currently chat restricted/banned/etc... or at most players who only recently completed their punishments.

For example, a player who got a 24 hour ban at the start of the season and hasn't gotten chat restricted, banned, or so much as given an automated warning since then for months and months, a player who for all intents and purposes can and should be considered completely reformed, should not lose his ranked rewards when he has shown a clear willingness to change his behavior and is now in line with the majority of players. The ENTIRE point of the concept of reformation is to turn offending individuals back into ordinary individuals for the betterment of themselves and others. This system is more akin to a system focused on punishment, not reformation. If the system Riot CLAIMS to be promoting is Swedish prison, they just sent anyone who has had ANY level of infraction this year, regardless of proof of reformation, to pound you in the ass American prison despite singing the praises of Swedish prisons from high on the mountains for months and years. It is a huge hypocrisy and discrepancy in their apparently false message of a new form of player behavior management and improvement, and makes all their supposed efforts look like a joke.