You're in the military, its part of the culture to always be on the look out for people milking the system. There is only room for those that contribute to the mission. Also, those that get to 20 years do so at tremendous sacrifice. There often is an unwillingness to help people gain retirement with less sacrifice than those who do 20 years.
I am not saying you are milking the system, or that you are undeserving of compensation. I am saying the judgements are present and it is wise to avoid them being laid in your direction.
Now, that being said, early in my treatment they asked me if I wanted to stay in or get out. I said I wanted to stay in. MEB was talked about a few times, mainly in how the doc can help me avoid one. When the time came, I called her up and said ok, this isn't working, lets do the MEB. There was no problems. However, me making it clear that it wasn't a goal and the doc letting me know it was a likely conclusion made the conversation ok.
Those who are perceived as hard chargers dedicated to the mission are treated better. You're already broken, they have been looking at you in a negative light for awhile if you unit is anything like mine. Fighting that perception is often more successful than giving into it. You know you are broken and you need out, how to you convey that and keep people on your side? Your mileage may vary, but from what I know of military docs, they want you on their side, with the mission being a successful recovery.