It's hard to argue with your logic. I've seen multiple cases of such talks happening and resulting in "happy estimations" and think it's all the matter of project management culture. This is very deep topic but it is possible to refer to two basic issues without going deep:
- 1. YOU are specialist and if you're saying it takes X time, management should listen. One way I used to measure programmers efficency was estimation/correction ratio and it quite worked (After working with people for at least 2 months I usually knew if they over- or underestimate work)
- 2. Uncertainty can be estimated and there are many methods to do this
I recommend the book Reinventing Project Management by Shenhar, Dvir if someone is interested (it describes approach models for various projects). I think it is important to acknowledge that not every organization wants to deal with delays, stress etc. - some are just what they are and are not willing to change.