The National ID card idea isn't being proposed as a convenience but as a tool to fight terrorism. The only way it can be an effective tool is if it's use becomes mandated in some way for a lot of day-to-day activities: to track movement, where someone lives and so on.
Else what purpose would it serve? In the US I don't think any of the companies that would stand to make a lot of money from such an idea gave particularly large amounts of money to our politicians so a political pay-off seems and unlikely motive. It might be done as a feel-good-at-least-we're-doing-something sort of thing. In that case I think the temptation to use it for purposes ostensibly noble and actually ignoble would be irresistable.