Syria another Western power move

The volatile Syrian situation is again in the international spotlight after more than 100 people, many of them children, were killed in the town of Houla on May 25, and an unknown number of civilians were killed in Qubair on June 6. After both massacres the United States and some Western countries immediately pinned the blame on the Syrian government before investigations had determined who was responsible.

Why are the US and its Western allies so determined to pin the blame on government forces?

Because, by doing so, they can put pressure on President Bashar al-Assad to step down.