Personally I am pretty convinced that bacterial infection plays a role
Brown Jelly Disease (BJD) is an issue many reefers have run into. Like most coral diseases, the pathogen causing BJD has not been conclusively determined. Here I will share some observations and test results supporting the idea that its caused by a bacterial pathogen, and so may be treatable...
www.reef2reef.com
I do agree that physical damage plays a role, opening an opportunity for infection. But I've sadly seen plenty of BJD without known or visible injuries. Followed by spreading of the contagion within the tank. Which makes me think a pathogen also plays a role. Based on my 16S sequencing there evidence that at least suggests a bacterial pathogen.