As for his attitude toward Athens, this is a bit more difficult to pin down because Thucydides' fellow Athenians had exiled him from his native...
Thucydides' attitude towards the Peloponnesian War seems pretty clear: it caused a lot of suffering and hardship for people on both sides of the fight.
As for his attitude toward Athens, this is a bit more difficult to pin down because Thucydides' fellow Athenians had exiled him from his native land for 20 years because he had failed to bring reinforcements quickly enough to the Athenian forces at Amphipolis in 423 BCE. Thus, it is difficult to imagine that Thucydides would have had any great love for the people who exiled him for 20 years.
It was also my fate to be an exile from my country for twenty years after my command at Amphipolis; and being present with both parties, and more especially with the Peloponnesians by reason of my exile, I had leisure to observe affairs somewhat particularly. I will accordingly now relate the differences that arose after the ten years' war, the breach of the treaty, and the hostilities that followed. (Thucydides 5.16; Richard Crawley translation)
Still, Thucydides does appear fairly objective in his account of the war. The Athenians certainly had plenty to be proud of, as Thucydides makes Pericles say in his famous "Funeral Oration" in Book 2:
In short, I say that as a city we are the school of Hellas, while I doubt if the world can produce a man who, where he has only himself to depend upon, is equal to so many emergencies, and graced by so happy a versatility, as the Athenian.
On the other hand, Pericles' claim that Athenians employed their riches "more for use than for show" would be a difficult pill to swallow since Pericles' audience could see behind their leader the Parthenon, which had been financed in large part with money the Athenians had acquired through their leadership of the Delian League, money which was supposed to be used to defend League members against the Persians.
Elsewhere, Thucydides is more openly critical of his fellow Athenians. He obviously takes some pleasure in noting that the Athenian commander Cleon died with his back to the battle. He also has harsh criticism to level at the Athenian demagogue Hyperbolus. Furthermore, Thucydides did not approve of the sort of democracy that was in place at the time of his exile, but does express clearly his preference for the rule of the 5000 that briefly held sway in Athens after the governmental revolution of 411 BCE.
Clearly, there are also some moments where Thucydides cannot approve of what his fellow Athenians were doing. The Athenians' inability to help their allies, the Plataeans, in 431 BCE clearly does not meet with Thucydides' approval. Likewise, the Athenians' bullying (and eventual destruction) of the people of the tiny island of Melos in 416 BCE is not something Thucydides approved.
In sum, while it is clear that Thucydides did not like the hardship that war inflicted upon his fellow Athenians, he also found several Athenians and Athenian actions of which he could disapprove.