Eh, I just see it as part of the fantasy. Trek's always been fantasy dressed as sci-fi to me. If emotionally suppressed humans with green blood and pointy ears are allowed, as are bright blue humans with antennae, then all sorts of slightly-modified humans are too.
Personally, I'd have preferred they just had more regular humans on different planets rather than adding the same pointless bumps to foreheads over and over. TOS had already established that an ancient super race (the Preservers) had transplanted people from Earth in centuries past.