Up-voting a comment does NOT bump the thread to the top of the "Active Forum Topics." You need to post a new comment to do that.
Up-voting a comment SHOULD be an indication that you think it's worth reading. It's a recommendation that other people read it. Doing that to a "bump" purely wastes their time. Personally, whenever I see a "bump" with up-votes, I down-vote it.
Recommended reading: The Most Dangerous Superstition by Larken Rose
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