There's plenty of difference between Syria and Iraq, Synthaholic.
1) Intelligence. Although it may have been false, we acted on what was at the time concrete intelligence that Saddam Hussein had WMD. Here in Syria, all we know is that some unknown force launched a chemical attack on Aleppo and the Gouta.
2) International consensus. President Bush had a full contingent of international support for an invasion of Iraq and Afghanistan. As opposed to Bush, Obama has none.
3) Congressional approval. In 2002, the Iraq Resolution passed 77-23 in the Senate and 297-133 in the House. Ironically then, 40% (82 of 209) of Democrats in the House passed the resolution, while 58% (29 of 50) them passed it in the Senate. Rumors are now that Obama does not have enough votes in either house to approve a strike.
4) Those who ignore their past mistakes are doomed to repeat them. Apparently Obama didn't learn well enough from Bush the consequences of not looking before leaping. We as Conservatives, Libertarians, and Republicans learned from our mistakes. You Liberals and Democrats continue to and insist on making them as far as Syria is concerned.