Why do Democrats oppose voter ID laws?

They want to cheat. 

Didn't need them before, DONT need them now.

We should require universal background checks for everbody who registers to vote. The FBI should check out every one that wants to vote to be sure they are fit to vote. That way we could stop foreign interference in our elections, and stop voter fraud.

Where I live, they issue a voter registration card that shows voting precinct and polling place, name & address.  That, along with a government-issued photo ID is all I need to check into the polling place.  Pretty simple stuff.  No one can vote for me and I am verified as a registered voter.

We DO have to show IDs to vote and have for years. The system works. The only reason to change it is to make it harder for people to vote for the 

OTHER party. I notice that no Republican bothers to mention all the other things in the voting-restriction bill, like removing drop boxes from cities (traditionally Democratic) and making it harder to vote by mail, done by the military (and Trump) for a long time.

We don't.  Where did you get that crazy idea.  It's called "voter registration".  We have that here.  You obviously don't seem to know much about the U.S.  Maybe your trolling would be more effective if you actually knew something about our nation.

The simple fact that IDs are not as easily available to all demographics. If we had a reliable method of making IDs universally available it would be an easier sell.

Of course, like Republicans, Democrats have a vested interest in voting constituents. It is an easier sell for Democrats because more legal voters are desirable in a democracy and that's what they're after while fewer voters favor Republicans-which, like their recent use of gerrymandering, favors them but is contrary to our National Charter of one man (person,) one vote. Like it or not, that is no longer restricted to males, landowners, or race.

Almost every single state already have voter registration and voter ID laws.

What Republicans are proposing are clearly targeted at suppressing voters.

Republicans have openly admitted that the more people vote, their chances of winning elections is greatly reduced.

It would prevent fraud ... something which a Dems rely on to win 

That isnt the only law being passed. do some research.