Can you give an example of a bill where Dems attached a universal free federal ID rider? I haven't heard of that before, and would like to research more. Most complaints about universal IDs in US are about a hypothetical
mandatory ID, but you don't need it to be mandatory in this case; just make it available free to any citizen that requests one. So I'm curious if Dems added a mandatory clause there, or if not, then how did Repubs justified voting against.
(Side note: I'm not opposed to a mandatory federal ID, personally. Given the existence of SSN, driver licenses etc, it's just codifying the status quo in a way that allows it to be implemented far more efficiently. If the feds are going to track me anyway, I'd rather them at least use that information to provide services to me in a more efficient way.)
As far as guns, for starters, it's a right to keep and bear arms, so we have to talk about licenses to carry as well, not just licenses to possess. These licenses aren't free in any state that has them, and can be extremely expensive in some, to the point of hundreds of dollars. And note that handguns in particular are the one type of firearms that was specifically cited as protected in Heller, so this can't be justified on the grounds that they're somehow exotic and outside of the scope of 2A.
But there are also jurisdictions where mere possession requires a license - for example, FOID in Illinois, or the NYC permits. Those apply to long guns as well. And they also come with fees - in NYC, you have to pay $140 just to make an application, and then another $90 on top of that for fingerprinting, just to own a long gun.
Then there are indirect fees imposed by various requirements. For example, most states with universal background checks implement them by requiring an FFL transfer with the usual NICS gate. But those are carried out by private dealers, who charge essentially arbitrary fees for them. Most laws do not set any limits on those fees. And since the check is mandatory, there's no way to avoid them, effectively requiring paying money to exercise the right to own. (There's some obvious irony here in those laws effectively subsidizing local gun stores, by letting them get a cut on every private sale, but it's a separate issue.) Same thing with mandatory training.
To be clear, I don't think that universal background checks or carry permits are bad, or even that licenses to possess are bad. As a gun collector, I'd actually personally prefer license to possess to the current NICS arrangement - it would certainly make my life easier! - and it's also more efficient at enforcement. The point, rather, is that charging for those checks and permits amounts to limiting a constitutionally protected right only to those who can pay for it, effectively turning it into a privilege. And in that regard, it is very similar to a poll tax, and I can't see how one can be opposed without opposing the other on the same grounds. I oppose both, and other similar arrangements (e.g. funding the justice system via court fees).