Which Cabinet Secretary? There are eleven of them. Presumably, you mean Angela Constance, who is Cabinet Secretary for Justice and Home Affairs. But the Cabinet Secretary for Justice and Home Affairs does not have the authority to dismiss the Chief Constable of Police Scotland.
The Chief Constable of Police Scotland is appointed by the Scottish Police Authority (https://www.spa.police.uk/who-we-are/the-board/) subject to approval by Scottish Ministers. Only the Scottish Police Authority (SPA) has the power to dismiss the Chief Constable.
This letter should probably have been addressed to Katharina Kasper who is Chair of the SPA's Complaints and Conduct Committee.
Five minutes-worth of research was all it took.
This is why Liberate Scotland has no credibility.
https://www.barrheadboy.com/liberate-scotland-press-release-letter-to-cabinet-secretary/
[This was submitted as a comment but may well be censored.]
They would do better simply to point out the diluting and damaging effect on Scottish culture and tradition of having the leaders of our public institutions dominated by those from firth of Scotland. This includes (but not restricted to) our universities, health boards as well as the police service.
Making it all about the head of Police Scotland reduces the debate to the personal and trivial.
Getting the process details wrong undermines the protest still further.
Your critique of the LS missive is absolutely valid in my humble opinion.