As the CSR's official Beatles nut, there is a defence for this.
Macca had just written and released, prompted by Bloody Sunday, a wee ditty called 'Give Ireland Back To The Irish' which was immediately banned by the BBC.
In a fit of pique he released 'Mary Had a Little Lamb' very quickly afterwards as an insult to the Beeb and as a two fingered gesture to the establishment.
Unfortunately, as witnessed by 'When I'm 64', 'Obladi-Oblada' etc, he's rather good at writing kiddy songs and this charted immediately, leaving behind it any vestage of political capital or biting wit.