Not all of the members are here so they can rank up fast ...
If there will be less members in the future, then I guess most of them will be the one that is here for the money and not the knowledge.
You are wrong. Spammers and account farmers will leave first because they can not or hardly ever rank up with merit system. Those users simply join the forum to get money/ Bitcoin. Then rest users of the forum will stay here to learn, to discuss, to contribute to the forum discussion, help each other; not mainly or only for getting money anymore.
All members of the forum will be much better and the spammers have proven to be reduced, this time everyone is getting focused and motivated to be able to contribute to the forum by making good posts and also useful for the development of cryptocurrency. merit has made the forum better and I think it will be implemented over a long period of time.