The poet reaches a truly dark place in this section of sonnets. 

Sonnet 66 begins with a suicidal pronouncement. The poet says "Tired with all these, for restful death I cry." 

And, following this terrible sentiment they issue a list of complaints. He is over it. The wrong people have power and if it were not for their beloved, the poet would leave the world.

This pain is enhanced by the poet's beloved being with someone else, someone unworthy. Shakespeare looks back to ancient times to find a world suitable to quality of his love for his beloved.

The problem for the poet is that inferior minds are seducing his beloved. He doesn't take credit for knowing that the beloved is beautiful, as that is common knowledge, but remains steadfast in their supposition that their love is different because it is true.

Adding more to the mix, it seems that in addition to being courted by other poets, the beloved has become a target of gossip and slander. The poet attempts to use this as a wedge to create a gap between their beloved and the other poets.