Power, opportunism, thirst for war, corruption (not oil though). Plenty of reasons for this war.
Your logic has a flaw though: It's not like Saddam would have just stopped doing his thing in 2003 had he not been removed from power. The country was a powder keg anyway, so perhaps it would have ended up just like Syria eventually (I can't imagine the Arab Spring leaving it alone) - or perhaps we would have seen another war between it and Iran. Another possibility would have been Iraq attacking a neighbor other than Iran again, perhaps at a time when they weren't expecting a harsh American response (e.g. under a Democratic US presidency).
None of this excuses that Bush and Blair made up reasons to invade the country nor the incompetent handling of it afterwards that led to most of the up to one million dead post-Saddam, but let's not pretend that everything would have been rosy had the second Gulf War not happened.
Why are you blaming Syria on America, even though it was internal unrest sparked by the Syrian government torturing a bunch of kids for anti-Assad graffiti? This resulted in increasingly larger protests, which were crushed with incredible violence by the regime, which in turn led to mass defections from the Syrian army as more and more soldiers were unwilling to kill their fellow citizens, creating factions that fought both against the Syrian government and among each other.
America caused none of this. In fact, it's the Syrian government that claimed foreign agents were responsible for the initial protests. It's not a good look to repeat this obvious and transparent lie.