Dianna Agron and Lea Michele are seen next to Cory Monteith in the saucy pictures which have been criticised for sexualising the actresses.
But Mark thinks critics need to realise that they are adults playing teenage school children in the musical-comedy.
The 28-year-old tells US KIIS FM presenter JoJo Wright, 'Personally, I think it's not a big deal, Lea is 23 years old [sic] and has every right to do that.
'I mean, come on! We're obviously not in high school, it's tongue-in-cheek that we're in high school.'
He added: 'People are starving, [football team Dallas] Cowboys are losing - there's more important things to worry about in the world.'