The intersection of internet memes and copyright law is an interesting area, and one where copyright law has not actually caught up to a changing world. There are several issues at play.

The most basic underlying issue is: Did the original creator of the meme do so legally in the first place (meaning, did the original creator use copyrighted images, and if so, was the use permissible either because of express permission being granted or through fair use)? The answer to that question is usually no - the vast majority of internet memes are probably "technically" copyright violations. I put the technically in quotes because in actual practice, if the meme isn't being use for a commercial purpose e.g. making t-shirt or coffee mug with the meme, etc., this usually falls into a gray area of non-enforcement.

There are one or two famous counter-examples - e.g. the "socially awkward penguin" meme used an image originally featured in Nat. Geo. and Getty images famously filed a takedown notice with a German blog for using the meme and demanded payment for the use. And as far as the text that is added on top of the meme, it is usually not possible to copyright a very short phrase or section of text in the first place even if that phrase or section of text was actually original to the meme creator (and again, in majority of cases, the text is also not original to the meme creator).

But this isn't what you are talking about - you seem to be saying, the post author should give attribution to the meme creator (who as noted above, probably used copyrighted material in the first place). So this is where we get into really gray territory. Unless the meme creator owned the image(s) used in the first place, slapping some text on top would not usually be considered creating something new that could even be copyrighted in the first place. And as noted, the VAST majority of memes are created by people who did not own rights to use the images.

So basically, the vast majority of meme creators are not truly "creating" content in the sense of a photographer who took a picture, or an author who wrote some text, etc. They are combining images and text that they did not have permission to use in the first place, and are doing so for the express purpose of sharing it and with the implied intention that it will "go viral", meaning be shared again and again. That is in fact the entire point of creating and sharing memes.

To say that someone should credit the original meme creator is completely missing the point of memes. It implies in the first place that the meme creator owns copyright to their meme (and in the vast majority of cases, and for the reasons noted above, this is not actually the case), and it also implies that sharing a meme without attribution is wrong somehow.. when that is in fact the entire reason the meme creator created the meme in the first place. Memes are created to be shared. It also ignores the fact that in the vast majority of cases, it is literally impossible to tell who the original creator of the meme was. When a meme goes viral and appears on thousands of web pages, there is almost never a trail of attribution to follow.

So, in short, while there are certainly underlying legal/copyright issues with memes, saying that someone should list the "original source" of an internet meme when the meme is used as memes are intended to be used, as a funny illustration of a point, to me, clearly falls into the "get the stick out of your ass" category. No offense.