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Friendly reminder that the rule is not to have -already- caught them all, but more that you intend to catch them all at some point.
The 'gotta catch 'em all mentality' simply means that one of your long-term goals as a Trainer is to fill your NatDex. Do not shun/ban friends who are well on their way to becoming a Pokemon Master; instead, hone in your spite on those heathens who would not 'bother' to achieve life's ultimate goal in Catching Them All.
Since I'm sure someone will ask, I have not caught them all yet. But I'm getting there, and I will. I gotta.