The Doctor, Polly and Jamie have been condemned to the pits, to the 'Danger Gang', for the crime of proving to the Pilot that his world is run by secret things that constantly order him to not notice them.
The trio are entering the pithead to begin their work as miners, mining the deadly gas that the Colony collects for its unseen masters. One of the Colony's jolly little work ditties plays in the background. A loud, insanely chipper voice sings lyrics about how happy everyone should be to work and serve the Colony.
The Doctor groans as if in terrible pain.
"What's the matter?" asks Polly.
"Ooooh, dreadful!" exclaims the Doctor, "Did you hear that rhyme? The man who wrote that ought to be sent to the Danger Gang, not us!"
The Doctor's concern isn't for the danger of the mines. It's for the ugly, crass, aesthetic banality of tyranny; for its kitsch horrors; for its lack of imagination. This might seem like a failure of proper priorities... until you remember that such crassness is a symptom of the infection in the social wound, the same wound in which the macra teem.
In a society that demands you work for hidden, secret, ineffable, insane masters that you never see and can't control, the mass-produced art that surrounds you is always going to be so much slop. Its function is to soothe, to reassure, to distract. It may not be consciously crafted to do these things, but if it doesn't do them it simply doesn't get mass-produced in the first place. In a world so riddled with secrecy and injustice that psychosis becomes a necessary feature of social life, the songs you hear on the radio are always going to hide repressed lunacies within their mindless platitudes. When you are expected to never question and never stop smiling, what chance is there that culture will be anything other than bland, safe, comforting pap?
And shitty, rubbishy, worthless, careless songs hurt us. Songs that side with power are injurious, especially if they're dripped into your ears day after day after day. Songs that are just ugly and dull, because they are made in the same way as spam, are just as bad. They hurt our hearts and souls and guts.
The Doctor's priorities are just fine.