Naive question, why wouldn't someone want a national ID card? From my understanding and time in sweden (granted only 5 months) they seem like a much better system than SSN
In the US, ID card policies were and still are often used to disenfranchise minorities from voting. The policies behind them are often inconsistently applied and sometimes require large bureaucratic efforts to rectify. Obtaining a copy of your birth certificate in the US often means going back to your home county and visiting some municipal office for hours on end. If you work a 9-5, there's no way in hell that's happening.
Voter suppression in the United States has had a long, sordid history. Blacks were given the right to vote after the civil war, prompting southern states to implement literacy tests, poll taxes, basically any legitimate-seeming test to de-facto turn away black people at the polls. This got so bad that we literally wrote an Amendment (24th) to state "yeah you can't do this either".
What's fucked up is that this sort of thing STILL happens. This past Tuesday, a number of voters in Virginia received calls telling them to go to a different polling station from the one they were assigned. See https://theintercept.com/2017/11/07/virginia-voters-get-myst...
Stuff You Should Know did a really good episode on voter suppression in the US that I'd recommend.
Historically, registries of citizen identities have been used for horrendous exploitation of the public. They have been used to ease profiling, targetting, discrimination, and elimination of anyone who is politically problematic. Personally, I resist most sort of formalization or systemization of human life or identity. Any person who says "our policy doesn't mention your situation" or "the software doesn't allow that value/have a field for that" and considers this to be a problem of the person with a life that doesn't fit the mold the designers of the system fantasized about really ought to be punched in the mouth, and creation of an easily-indexed national ID is an important step in such systems.
Why do they want a NUMBER? Because names are too... human. They're messy, and they can change, and they don't fit standard forms. It's an impulse to purge the humanity from social identity that motivates establishment of national ID numbers.
In the US at least, in theory the proposal for a long time was just to not keep track of people in the first place. The federal government collected taxes on things like property and tariffs that were hard to avoid, they performed a census once a decade to get a rough idea of how many people there were, and anything beyond that was none of their business.
Then we got income taxes and federally guaranteed pensions (Social Security) and medical assistance (Medicare/Medicaid) and a few other, smaller safety net programs. Furthermore, while there's plenty of fighting around the margins, the overwhelming majority of Americans are broadly in favor of keeping at least some of the Great Society programs, and that means we have to have a national registry of some sort.
It turns out that when the population is broadly distrustful of the idea of a national registry but broadly in support of a tax regime and social programs that require a national registry to function the stable equilibrium is a really really shitty national registry that everyone hates but nobody feels they can improve without getting shouted out of office. American politics is dumb.
That is the whole point. Some cultures have residual beliefs about limited government and privacy. Some sub-cultures and families in those cultures have maintained a strong believe that no one should be "keeping track" of them.
Based on your phrasing it sounds like you think owning a national ID card is commonplace in Sweden. The national ID card system isn't widely used at all, most people use either their drivers license or passport when they need to identify themselves.
The only thing everyone has is a person number, and the difference is that it is explicitly considered public information and you can get anyone's person number by just asking the Tax Agency. It's just a convenient way to keep track of people, not a way to actually identify yourself.
