The "something" is a consolidation of federal power. The US is not a unitary state like most of the countries in Europe. The states hold a lot of power individually, and many want to maintain that as much as possible. The rules around identification are something that is significant to how people interact with their government and people do not want those rules to be decided federally when they can maintain that power locally instead.
> The "something" is a consolidation of federal power.
Ok but I still don't understand what power are you consolidating here.
If the federal government decided to issue an ID card valid for all citizens, what's the issue?
You already have something that work that way and it's the passport.
Now, I know that having a passport is not mandatory but if tomorrow the US government decided to issue passports, for free, to all citizens, would that be an issue?
A passport is only used for international travel, which was already under the purview of the feds. It is also only used for travel, which means that many people don't have one.
Drivers licenses (/IDs) are used for everything else pertaining to someone's daily life. In this way it affects how/who/where/when people drive, vote, buy and sell controlled things, engage in some financial transactions, travel domestically, obtain social benefits, etc.
It allows local authorities to be gatekeepers. A commonly used and carried federal ID would shift that gatekeeping authority to the feds. It could also enable additional gatekeeping which is not currently possible in the absence of this ID, which is a primary concern of the people who are against this.
