This is my first time wading commenting on a TB discussion, so I ask for a little slack if I'm too far off base.
I'll start with that I would be strongly opposed to any sort of posting limit for MR. As someone who only recently passed the 180/180 mark so often quoted (sometime within the last week), who has made many posts in MR, started, by my rough guess, half a dozen decent MR threads, and made solid contributions to another at least half dozen, any sort of post limit on posting in that thread would hurt the overall community. I'm fortunate in that I discovered ITA Matrix well before I discovered FT, so I very, very quickly got up to speed with finding MR deals and manipulating them where possible. With a 180/180 limit, I would have not been in that forum until this week. How many people, even once they pass the 180/180 mark, end up visiting OMNI or CC? I would bet a good number of them do not within any short period of time after qualifying to see it. I would also argue that MR is far more directly related to the main goal of FT than OMNI or CC. Those are privileges for contributing members. MR isn't a privilege in the same way to me. MR is a major part of FT, and any major restrictions on it would be far more harmful to the community than it would be without those restrictions.
As for requiring a simple login, the only opposition I can raise is for a member, say at an airline lounge computer or public access point, who may not wish to login with their FT account to assure that their FT login and password are not compromised due to a compromised computer. I personally use a different login and password for FT from any other login/password for this reason, so that even if my account is compromised, nothing else is due to it. The only true way to "protect" a deal is not to publicly post it. The major example of this is the trick it thread, where many things are not publicly posted, and many things are heavily coded. Once someone posts a deal publicly, it is unprotected. When I come across one personally, I first check it against my dates on which I could use it. If it makes sense for me, I book it myself, then post it. If not, I make sure it is bookable somewhere, and then post it. I try to provide as much detail as possible so other members may more easily book it.
I would not say I am opposed to a login requirement for Mileage Run, however I am not sure what the overall effectiveness would be. I feel it may keep deals alive at best 10% longer, maybe a couple of hours at most. A true mistake fare will be seen by enough FTers and posted on a blog quickly, rendering the login requirement useless. The fare would likely disappear before it could be picked up by a Google web crawler or anything like that. As GUWonder said, we may need to define what "protecting" deals consists of. Then we will want to decide if this would help achieve that goal. I am undecided on this personally. I feel it won't hurt to try this, but it might not make a major difference. The key is making sure that it does not negatively affect the community. I honestly do not see a major impact either way. As long as this is not the precursor to a post/time minimum, I would say I am in favor, as I do not see a major negative effect.