The beginning of the merit system was a bit weird as a lot of people didn't understand exactly what it should be used for (some don't know even today). I bet a lot of people were just playing with them at that point and didn't understand what it's true purpose was.
I even remember someone getting 50 merit for calling the other a "butt hurt idiot" which was simply stupid.
There still are some cases like that and when you see it, you definitely get discouraged.
Take a look at this post:
https://bitcointalk.org/index.php?topic=5029917.msg45811067#msg45811067 he essentially said nothing but still got 20 merits. There are a lot of 1-2 line replies (that do not bring any value) that are also rewarded with high amounts of merit.
You can find a lot of those here:
https://bitcointalk.org/index.php?action=merit;stats=topreplies , it's a bit sad.
For example, I have created a guide to exchanges where I invested a lot of time into, but was not seen as "important" as other discussions here:
[Guide] Best/Top Crypto Exchanges: Fees & more. I think it also has to do with making your posts visible enough to others but I do get discouraged when I put in the time and don't receive merit.
Please keep in mind that merit is not moderated so, you can talk all you want about the abuses and nothing will happen (other that a negative trust maybe).
I think you should focus on making the best posts you can and not worrying about the "this noise" because it isn't really something you or I can control.
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I know someone may bring this arguement that any individual can give merit according to his/her discretion but the point is Legendary members are not ranking up to any further rank so why dash them that huge number of merits when there are other lower rank members who equally deserve to rank up with some quality post of theirs.
I personally try to avoid meriting Legendary users, not because they don't deserve merit but because they simply don't need them to rank-up. I prefer to award merit to people who actually need it.