Syrian conflict: some questions

1) Now, it seems, Assad in Syria (or someone else?)is killing people with gas, and it is unacceptable. First the various factions killed with bombs, rockets, guns, etc.. This was acceptable? 2) Whose side are we on? It seems that the rebel groups is quite varied among different factions, there are also those linked to Al Qaeda. Nobody seems much reliable, or able to guarantee stability or a minimum of democracy. 3) How many "collateral damage" (innocent civilians killed) will be made before realizing that we put ourselves in yet another dead end? 4) If acting does not change the situation or or gets it worse, if possible, it isn't best NOT to intervene?