Objectively speaking, there are some strong points for people on the inside:
(1) The house to house preaching - as far as I'm aware, they completely blow any other religion out of the water with the extent of the ministry. When they look in the NWT bible and it uses the words "house to house", this seals part of the deal in their mind that they are in the right religion. Of course they cannot connect the dots that "if what I'm preaching is wrong, then this is all null and void". But from a numbers and participation standpoint, it is quite impressive.
(2) General Behavior: The members are so indoctrinated, lots of them follow the rules quite strictly. In public, they don't curse, don't steal - from a broad viewpoint non-witnesses will often think they are pretty nice people.
(3) The general idea that "this is the real truth about God and therefore his entire organization believes exactly the same". This was a hindrance to me leading up to me taking the step to actually admit that I was wrong. So many different churches believing so many different things - I just knew that everybody can't be right. So the "perceived unity" of the JWs was a strong force for keeping my doubts in check.
Those are just a few things that seem to have a hold on lots of Witnesses. I'm certainly not taking sides with WT, but trying to be non-biased in my observations.
-mentallyfree31-