It would be great to think that in the startup industry, people would realize that today's junior person could become "big time" tomorrow, and that you should therefore be meritocratic and respectful to everyone. But that's not my experience.
In my experience, people who look down on more junior people in the startup industry are either douchebags, or outsiders. Everyone in the industry understands that where someone is today is often uncorrelated to where they will be tomorrow, and acts accordingly.