Can you name one city or town in the US that is dependent on Amtrak for basic transportation? For instance, is there a single town anywhere in this country that doesn’t have a highway or airport but does have a train station with Amtrak service?
So this isn't about providing people with access to transportation, because people do, in fact, have access to other transportation options. It's about catering to the whimsical preferences of people who like to ride trains. I don't think catering to those whimsical preferences is a necessary public service.
Exactly. And the pros and cons for trains, as a mode of transportation, have made them a less viable option for most American journeys ever since the mid-20th century. When you say "there are people who do not drive or fly but use trains", you're not describing the typical, reasonable person who weighs the pros and cons between different modes of transportation, you're describing someone who refuses to even consider alternate modes of transportation. Maybe it's not necessarily a whimsical romanticism for trains, but it's certainly something well short of any actual necessity that's deserving of public subsidy.
These things should be done exactly because they are not the norm. There are people in unique circumstances in every corner of this country who rely on niche options. I know some of them who have relied on these things. The free market can take care of “normal” people and circumstances just fine.
USPS has a universal service obligation but also a legal monopoly. Meaning that if you try and start your own postal service, the feds will literally shut it down and throw you in prison. Its probably no coincidence that USPS also has abominably nonexistent spam filtering, to the degree that the majority of USPS service I’ve received in my entire adult life consisted of myself throwing away and/or shredding the vast majority of crap that they shove in my mailbox six days a week. And any suggestion that maybe they cut down to shoving crap in my mailbox 5 or even 4 days a week is treated like it would be the end of Western civilization.