Medicare is a form of welfare, just branded differently. It's a means-tested benefit funded in a pay-as-you-go manner via income tax just like any other. The means are just different amongst various programs.

Are there any actual cases of making more earned income via a regular job worse than taking that extra dollar of pay? I'm guessing a few very rare corner-cases exist, but I can't immediately think of any. I imagine they would be somewhere in the neighborhood of the EITC or AMT type things.

That's dealing with Medicare, not taxes.

And basically, as your income goes up, so does your Medicare premium.