It's not about having an ID card per se, I wouldn't mind having to have one (or everyone having to have a passport). It's about what the police can then do - can they demand to stop you and see your ID card at any time? What's the punishment if you don't show ID? Those sort of questions are what make people nervous.
You don't have to carry your ID with you at all times, but if you've got nothing to hide, why not? A quick bit of research and I see you have to be able to show your ID to a police officer or at a police station within four hours of being stopped. (https://www.gov.uk/foreign-travel-a...u must be able to,places in France is illegal.)
But is that your experience in France? My understanding is that apart from making life simpler at immigration controls between European countries, ID's must be produced to an employer in order to get work and employers have a duty to register new employees against the threat of (possibly) criminal sanctions.
Yep...I have only ever been asked for my ID when crossing borders, or during the height of COVID restrictions when we were only allowed out for an hour's exercise each day. The police don't wonder the streets demanding to see your ID for no good reason. Also, as you say, anytime I have started a new job I've been asked for a copy of my passport and post-Brexit a copy of the titre de sejour (work permit equivalent).