It is a pretty complicated situation where both sides have very valid points for the positions that they are taking. See the very rational counter-points to your points. Not saying I agree with all of this, but it is a very valid line of thinking.
To your first point, they are not trying to take it away, they are trying to make it more inline with the refs situation. They want to move from a defined-benefit pension plan to a 401k. A benefit that is way more in line with a person who is working part time and is only doing it as a second job to their real jobs. It doesn't matter how much the NFL makes, it is a matter of what is deserved, and part time employees who's priority isn't even being a ref do not deserve a pension.
To your last point that is simply not true. Refs get paid if they are working games. All adding to the total list of Refs would do is add a so called "Bench". The Bench guys don't get paid unless they work a game. So there would be ZERO taking away of pay from current refs by adding more refs to the system. The only way a ref would make less is if they unperformed and get replaced by a bench ref. Meaning the total amount of pay will stay exactly the same even though there are more refs.
As it stands currently the refs who are doing this as a part time second job have zero accountability. Sure they have a grading system but that is only on place to figure out who will get bonuses by working playoffs. Coaches can get fired, players can get benched, so why shouldn't the Refs be under the same accountability, of which they currently have none. And they don't want any part of it now, and are actually scared to death of it, and would fight for not letting the bench happen more so then any other point. Think of it this way and it is something I heard on the radio recently,
"The league wants to be able to pull struggling officials during the season and hopes to change the system from one of “entitlement” to one of “accountability.” Unsurprisingly, the referees are resisting this. If you were an NFL referee, wouldn’t you do everything you could to hang on to a part-time job that paid you $149,000 a year, along with a pension plan, and came with little threat of being replaced mid-season"
If the refs would just accept the idea of more accountability I am more then willing to bet the NFL would start budging on other issues they are being thick headed with.