You are new here, so welcome to Meta Math.SE.
I've downvoted your post to show disagreement with your request. That is not a criticism of your post per se, just the way that voting on Meta expresses agreement or disagreement on proposals.
If you are not satisfied with the status of a seven year old Answer on the site, it is certainly possible to do more than merely Comment. You could post a new Answer, referencing the previous one that you think has a "mathematical error".
There are several reasons not to do so regarding the particular post you linked to above. Besides the fact that the so-called error is now seven years past, the wording is only subtly different in egreg's Comment. Concern over someone who could not appreciate the difference for themselves is not likely to be mitigated by incorporating that change into someone else's post. Indeed it seems likely to me that most casual Readers would interpret "infinitely many values" (in a sequence) to mean "infinitely many distinct values". So I don't think that the original poster (of the Answer) necessarily feels it has to be changed; making a change needs to be weighed against bumping the Question for a modest edit.
That Answer provides a slightly different illustration from the one in the Accepted Answer. I'd expect it would be a careful Reader indeed who would spot the difference, and I congratulate you on being such a Reader. But the principle here is to respect the meaning and manner of expression of original posters. If you want to frame the same example in a better light, you are welcome to do so, and perhaps be rewarded for your efforts. In the meantime it's good to ask here about the site policies and software to that your participation in the Community can be productive.