Peter is indeed angry even at the beginning of the opera, but not because he is ‘a thoroughly nasty piece of work’. He is angry because the local gossips have slandered his character, believe only their version of events, and will not listen to the truth. These are the themes that are developed from the very beginning, and in the exchange between Balstrode and Peter at the end of the first scene, the truth about the boy’s death comes out;
BALSTRODE
Then the Crowner sits to
Hint, but not to mention crimes,
And publishes an open verdict
Whispered about this "Peter Grimes".
Your boy was workhouse starved -
Maybe you're not to blame he died.
PETER
Picture what that day was like
That evil day.
We strained into the wind
Heavily laden,
We plunged into the wave's
Shuddering challenge
Then the sea rose to a storm
Over the gunwales,
And the boy's silent reproach
Turned to illness.
Peter has the chance of love, peace and perhaps even prosperity with Ellen, but he would only marry her for love, not for pity - there is courage and nobility here;
PETER
We'll sail together.
These Borough gossips
Listen to money
Only to money:
I'll fish the sea dry,
Sell the good catches-
That wealthy merchant
Grimes will set up
Household and shop
You will all see it!
I'll marry Ellen!
BALSTRODE
Man - go and ask her
Without your booty,
She'll have you now.
PETER
No - not for pity!...
BALSTRODE
Then the old tragedy
Is in store:
And as Balstrode’s response indicates, Peter cannot avoid the tragedy that will now unfold; just as in Oedipus, the tragedy pivots on the ambiguity between unavoidable fate (with an obvious hint to Britten’s homosexuality), and character flaws which are influenced by those around Peter (with equally obvious hints of homophobia), as it races towards the inevitable. Now the great Bear and Pleiades is Peter’s realisation that he is trapped, that he cannot make a fresh start, that he will always be an outsider;
Who can turn skies back and begin again?
This is why I think Peter must be sung in a way which brings out this conflict and ambiguity. A reading which emphasises malevolence and anger may well be powerful, but will miss the ambiguity which is the essence of the tragedy, in my view. No wonder Britten did not appreciate Vickers in this role.