How the data is collected, maintained and who has access to it and for what reason is.
The ID card scheme was utterly utterly illiberal and a complete white elephant.
If all it was was an extension of the NI card and/or driving licence I'd have absolutely no problem with it.
That said, I doubt you heard much about that on the stump either.
Total number of times ID cards mentioned to me in recent election - zero
I'm glad to see we agree that ID cards are not a civil liberties issue and that what you do with ID cards is potentially a very grave civil liberties issue.
Too many "liberals"* confuse neutral things like ID cards with utterly illiberal things like the "sus" laws that David Cameron admitted he was keen on a few years back and that the government is slyly working to bring back in practice if not in outright law.
ID cards, and more importantly the data that underpins them, are potentially an enormously powerful tool to revolutionise the delivery of public services. Other countries, ones generally considered to be very liberal, use them in this way. So should we.
I do not like ID cards, but on balance I think the benefits outweigh the costs.
* liberals with a small l, which for all our differences would probably include both of us.
If there must be trouble, let it be in my day, that my child may have peace.