Very much this. It is plain unhealthy how many people perceive copyright as being a 'measure to ensure income for artists'.

Hmm, at least in the US, the relevant sentence is: "To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."

The way I read it, the intent of latter half of the sentence clearly is to enable artists to profit from their works. Note that it does not say "all artists shall be paid no matter what". But by having exclusive rights to their works, it can work roughly like any other property in a capitalistic society: that is, artists may be able to capture rewards proportionate to the amount of the value they provide.

I am not a legal scholar, but to me the intent of the latter half is clearly stated by the first half: "To promote the Progress of Science and useful Arts".

One way to promote scientists and creators is to allow them to warn money so they can keep sciencing and creating.

Nobody is arguing that. What people are arguing is that if copyright does not promote the progress of science and useful arts, it fails to fulfill the intent of its existence. The follow-on argument is then that indefinitely extending copyright undermines that promotion of progress. If you buy both arguments, then you see why many people find the extensions so objectionable on Constitutional grounds. I don't think many people disagree with the first argument, because it's right there in the text (which is the point I believe your parent was making), but of course lots of people disagree with the second argument, believing that longer copyright terms better promote creation.

That's obvious, but the more interesting discussion (which we're really here for) lies in the unstated part of the sentence: how were the actions stated in the second half intended to result in the goal stated in the first half?

Don't you think that authors who release their work freely under copyright believe that yes it actually is a 'measure to ensure income for artists?'

I think that a large majority believe that it is to guarantee that their descendants receive royalties for all eternity.

Or...maybe some payment to themselves for their work?

What do you do with payments after your dead?