As Badger said, you can't define civil liberties as only being true civil liberties if we go as far as you.
Most people do believe in holding people without charge, the problem is for how long. Even the most pro-civil liberties person is going to agree to some amount of time for the police to write out reports and interview witnesses.
The point is the more you define civil liberties, the more you will push some of the people who did agree, into not agreeing with you.
A campaign is ALWAYS about weight of numbers. The more the merrier.
The wider you can make the banner, the more people will stand under it.
On a single issue, 42 days, a lot of people will stand under that banner, you bring ID cards into it, you bring 28 days into it, you bring Human Rights into it, you will just push more and more people away and the protest will be a few people in cagols standing around in the rain.