Very good thought...
There is also one more important aspect:
People who make negative bag-related comments are not initiating the dialog, they in fact are responding to a communicative signal already given (unadvertedly or deliberately) by the bag wearer.
The whole point of owning/showing those bags is their exclusivity, huge value and status symbol nature. Nobody would buy a Birkin to wear on a desert island. It is the reactions of other people that make the H. bags so desirable. They make the owner come across as well off, successful, dominant, lucky etc.
Therefore we must realise that by wearing such a hugely expensive bag, unthinkable to have for most people, a person is in fact giving out a loud non-verbal massage.
Humans are very tuned-in to non-verbal communications, and wearing a bag is actually a form of a non-verbal statement.
Whether the bag-wearer wanted to make such a statement or not, does not matter, the statement is still given out : "I am holier than thou, I am rich, I am cool, I can splash £10K on a bag to carry my umbrella in, you poor guys must envy me, you will never be so lucky as I am", bla-bla-bla.
Many people react to such non-verbal statements by disgust, and respond to it by some negative (or implied-negative) comments.
This is nothing to do with jealosy, envy, etc. Many people believe that having so much "extra" disposable money makes a person able to do something worthwhile: help a school, or pay for someone's life saving surgery... They believe (rightly or wrongly) that it is selfish and unreasonable to spend all this powerful money on a bag.
Those people see that the person shows off their wealth/status/demands attention - so they give that person this attention, in the negative form.
If our wealth is nobody's business, why do we show it off. If we choose to demonstrate that we can spend on such a bag, it is a statement that we are happy to proclaim in public. Therefore it is only fair if people respond to this non-verbal proclamations by stares (non-verbal disapproval) or verbal comments.
If one looks at the comments from this point of view, these comments cease to be offensive, but become a conversation which can be ignored or respected.
Of course, a true friend would never make a negative comment about a bag. But by the same token, a true friend would not turn up to a meeting with a friend who does not approve extremely expensive bags, with a Birkin.