It doesn't do anything of the sort. Every country in the World has rules about what documentation it requires foreigners to have in order to enter the country. Neither the UK nor the EU is any different in that regard. The lesson to be learned from this is (a) the importance of checking that your passport/documentation/etc. meets the rules of the country you are going to visit BEFORE you set off, and (b) that maybe the airlines and travel companies should be a bit more upfront about reminding passengers in advance what documentation they will need.
Well, if it hadn't been for Brexit, it wouldn't be a consideration for the UK - so it is correct to partly blame Brexit for this. On its own, it's little - but combined with all the other problems and inconveniences Brexit brings, it all adds up.
It is also non-obvious, though, so I agree that it should be stated in big red letters whenever you book a travel ticket.
Common sense would suggest that a printed expiry date is the correct expiry date (in the same way that the expiry date on any other document should be assumed to be the correct expiry date) so any variation to common sense needs to be made absolutely, glaringly, screamingly obvious - otherwise you are going to get people losing a lot of money on forcibly cancelled holidays.
It's certainly a lot less obvious than the liquids rule.
Showing a railway ticket to prove your contractual right to use a service isn’t at all like showing a passport. When you present yourself at the border to a foreign country you ask to enter as a guest. You have no absolute right to enter most of them at all, or to stay.
That you feel showing your British passport to a foreign border official conveys the same level of entitlement as someone who has paid money to use a service is quite odd.
It’s true that some border formalities feel more or less friendly than others, but in my experience it’s just one of those things. It’s two minutes out of your day.
I think this boils down to the old chestnut of "is freedom of movement a good thing, or is it not?"
From my perspective I would argue that, in an ideal world, there
should be an automatic right of entry to the majority of countries for a short-term period subject to certain conditions, i.e. you're not a criminal, wanted by the police, previously been banned from entering for one reason or another, or on national security grounds (e.g. you're a citizen of a "hostile" country). But I am a strong believer in FoM (and I personally would have extended it to selected countries outside the EU, not taken it away) and a strong critic of hard borders between "friendly" countries, while others will disagree. However, neither point of view is fundamentally right or wrong.
I realise the train (or more correctly, railway property) comparison is not such a good one as you pay money to use the trains, whereas you don't (well, directly at least) pay to enter another country. However, there are similarities. You have no "absolute right" to enter railway property or board a train; this is subject to various conditions. I was drawing attention to the fact that both involve entry to a "restricted" area, entry is subject to various conditions, and you can receive an entry ban (for the railway this might be due to previous misbehaviour).
Perhaps entry to a pub is a better example. Some pubs require you to show ID. Fine. But if a pub started taking fingerprints (for security reasons, to prevent barred individuals entering) I think most people would go elsewhere!