A lot of things bugged the Psalms writers, but there was one thing that really pushed them over the edge: idol worship.
By declaring idols uncool, they were trying to start something big. Really big. After all, idols were very culturally present in Israel.
The idols of the nations are silver and gold,
the work of human hands.
They have mouths, but they do not speak;
they have eyes, but they do not see;
they have ears, but they do not hear,
and there is no breath in their mouths.
Those who make them
and all who trust them
shall become like them. (135:15-18)
People believed their idols had powers, but the Israelite writers were trying to place a new kind of value on human life. Humans were created in God's image in Genesis, and so distortions of that image were not taken well.
Idol worship can be a touchy subject today, even within Judeo-Christian religions. For example, people will argue till they're blue over the appropriateness of Catholic saint statues. The Israelites wouldn't have been down with it, that's for sure.