Something being overlooked

Three judges at Scotland’s supreme civil court issued a declaration that the blanket ban on convicted prisoners voting was incompatible with their human rights.

BBC, Court rules on prison voting ban

Ok then, and this:

The move follows a ruling by the European Court of Human Rights which found a blanket ban on prisoners voting was a breach of their human rights.

BBC, Prisoner vote consultation begins

Here’s what I don’t understand. The impetus to allow prisoners to vote is coming from human rights legislation but surely once you’ve accepted the terrible trampling on the right to liberty involved in being banged up, why get worked up about something else so relatively trivial?