I think there is maybe a one in a million reason why I would do this, otherwise I don't think its acceptable for any reason whatsoever, and certainly not just because your baby was asleep when you got into the car. When we recently went on holiday we left the car at the airport in long term parking, and then took trains and walked to our hotel at our destination. I wouldn't drive with my baby unrestrained at home so I don't see why it should be ok to do it when I'm away - taxi or not. The parking cost us a fortune but it was nothing in return for the peace of mind it gave me that my girls were as safe as they can be while travelling.

I find it really difficult to understand how people can consider convenience more important than their child's safety.