Not sure why you think a trigger provision will not lead to the public option.
The condition for not implementing the trigger is that health costs must come down. There's no reason to think that health costs will come down in the private sector without reform...which is why many think the trigger will be inevitable.
I agree with you that the left is going to be pretty mad if only the trigger passes into law with no public option.
The devil would be in the trigger option details.
I'm not confident that Lieberman or Snowe won't fall for some inevitable trigger.