Read things over the years only to find out later that it didn't happen or it was exaggerated. I'm wondering how true this is: Athenians were bored. They needed a heroic cause so they could preform heroic deeds. They decided to attack Sparta. Vote was taken and passed. Led to a big disastrous war which Athens lost after decades of fighting.
This was cited to show that democracy is not always a good thing.
This is absolute bogus. The Peloponnesian War was the result of a complex and long-range political development centered around the two big confederations of the region (the Delian League led by Athens and the Peloponnesian League led by Sparta).
Let me offer you a deal: I will go into further detail, if you tell me your source for this hypothesis - it's much more interesting and easier to answer such a thing if you know the context and have some more arguments to directly respond to.
After Sparta and her Allies had effectively declared war and but before any fighting had taken place, Sparta had sent envoys stating that if Athens would make some small concessions they would not invade. Pericles the defector leader of the Athenian state at the item argued that if they were to make a small concession now under the threat of violence then they would be asked to make a much larger concession in the future. The assembly agreed and voted "no" on the Spartan Offer. By modern standards and without the value of hindsight, this would have been the only rational response.
I also want to point out that, that after the first decade of fighting when both sides had signed a peace treaty, it could be argued that Athens had "won." In the "Paradox Grand Strategy" game point of view with Athens having a higher internal stability, and revenue. With Sparta Sparta having lost some prestige and beginning to crack from internal tensions. Definitely nothing decisive. It wasn't until after Athens had botched Sicily, and Sparta and Perisa decided to pounce on a weakened Athens that the city was beaten.
The Athenian government was able to effectively prepare and prosecute large a pan-Hellenic wars. It was the failure of the Leadership of their Individual General in Sicily, that allowed a single defeat to turn into a crippling route. Even then it took almost another decade for both Persia and Sparta to take down Athens. The Athenian Government and the Assembly in particular had its systemic issues, but it was rational and consistent enough to keep it a major player in Eastern Mediterranean affairs for over a century.
Books to read are Thucydides Peloponnesian War and Xenophon's Hellenica.
Thucydides, in his The Peloponnesian War (my translation is the simply amazing "The Landmark Thucydides") says:
"The real cause [of the war], however, I consider to be the one which was formally most kept out of sight. The growth of the power of Athens, and the alarm which this inspired in Sparta, made war inevitable." 1.23.
What Thucydides explains as the beginning of the war starts with the city of Epidamnus, a distant colony of Corcyra in modern Northwest Greece. The Epidamnians overthrew their leaders..."the exiled party joined the barbarians, and proceeded to plunder those int eh city by sea and land; and the Epidamnians finding themselves hard pressed, sent ambassadors to Corcyra." 1.24.
Corcyra did nothing, so the Epidamnians asked Corinth for help. Since Corinth disliked Corcyra for a long time, Corinth decides to send help. The colony of Epidamnus was surrendered to Corinth, and Corcyra got pissed and launched forces to take back their colony. They eventually reclaimed their colony. Where do Athens and Sparta fit into this, you ask?
Corinth sent a new fleet to liberate Epidamnus, but Corcyra asked Athens for help. Corinth asks them, too, but Athens sided with Corcyra. Soon after, Athens laid siege to a city called Potidaea, a colony of Corinth. Potidaea, and a bunch of other city-states, denounced Athens to a Spartan assembly. Sparta invaded Attica and declared war soon after.
There are a lot of details left out (such as the indignation Athens created when it moved the Delian League's treasury to Athens and the repercussions from that), but basically Athens was growing so powerful that Sparta (and other city-states) feared Athens would take over all of Greece.
I recommend reading Robert Strassler's The Landmark Thucydides for the full picture. It is truly an amazing book with tons of maps that gives a great translation of Thucydides' account of the war (in which he fought for Athens).