Given that I've repeatedly said I don't advocate an intervention with troops or unilaterally, the first two points would be null - like in Libya, a successful intervention would not equate to war. Go back and read my very first post: my complaint was about China and Russia vetoing a Security Council resolution to condemn Assad. Were such a resolution passed, it would give international legitimacy to a Western intervention, carried out multilaterally, much the same as in Libya.
In regards to points 3 and 4, yes, I would agree. Collateral damage and escalation are dangerous, but collateral damage could be considered a necessary evil because as of right now, the situation is so dire that inaction would mean prolonging the war. So either way, whether there is going to be collateral damage, the question is whether it's better dealt in ousting Assad or not.
Finally, your last point: outcome. The fact is, you don't know who or what will come into political power. But if Libya, Afghanistan, Egypt or Iraq are any indication, the powers in place, while no large success, are *certainly* better than what they replaced. Like I said before, had the United States *not* taken a role, we wouldn't have seen the fledgling democracies, immature though they may be.