Only thing we can do is educate people like this by showing them that we can tank very well. I think this attitude just comes from ignorance - either from people who have never had a brawler tank for them, or from a brawler that has never tanked.
I've had it a few times where some scout thinks he can tank better than me, so I let him. Then when I pull aggro off him (opps forgot to cancel my hate proc!) 
and they start to see that we arent as bad as they thought.