> Here's my fave
>
> "A man's maturity consists in finding once more the seriousness he had
> as a child at play."
>
> I think it's Nietzche.
Dissolving the aspects of mind that enable reason to replace instinct as the source of desire won't produce activity aimed at mere innocuous amusement, will it? The insight in Nietszche is that when this is done what will get acted out is an unrestricted sadistic will to power.
“To practice cruelty is to enjoy the highest gratification of the feeling of power.”
An associated insight is that the kind of "reason" at work in the version of "materialism" dominant in modern "science" is a hiding place for this sadism. He thinks (self-contradictorily, according to Heidegger) that this "science" will, ironically, destroy all barriers to acting out by destroying any rational ground for limiting instinct (i.e. the kind of "reason" involved has "positivism" as one of its logical implications - radical skepticism is another of these implications) and by demonstrating that what we are "naturally" is the "cruelest animal."
Marx is at the opposite end. His "materialism" is radically different from the one Nietszche mistakenly identifies with "rationality" per se.
Like Aristotle, he understands childish play - "mere amusement" - not as an end in itself but as instrumental to the "serious" activities productive of the highest forms of pleasure and happiness. This is the ground of his dissent from Fourier's conception of ideal activity as "mere fun, mere amusement."
"It seems quite far from Smith's mind that the individual, 'in his normal state of health, strength, activity, skill, facility', also needs a normal portion of work, and of the suspension of tranquillity. Certainly, labour obtains its measure from the outside, through the aim to be attained and the obstacles to be overcome in attaining it. But Smith has no inkling whatever that this overcoming of obstacles is in itself a liberating activity - and that, further, the external aims become stripped of the semblance of merely external natural urgencies, and become posited as aims which the individual himself posits - hence as self-realization, objectification of the subject, hence real freedom, whose action is, precisely, labour. He is right, of course, that, in its historic forms as slave-labour, serf-labour, and wage-labour, labour always appears as repulsive, always as external forced labour; and not-labour, by contrast, as 'freedom, and happiness'. This holds doubly: for this contradictory labour; and, relatedly, for labour which has not yet created the subjective and objective conditions for itself (or also, in contrast to the pastoral etc. state, which it has lost), in which labour becomes attractive work, the individual's self-realization, which in no way means that it becomes mere fun, mere amusement, as Fourier, with grisette-like naiveté, conceives it. Really free working, e.g. composing, is at the same time precisely the most damned seriousness, the most intense exertion. The work of material production can achieve this character only (1) when its social character is posited, (2) when it is of a scientific and at the same time general character, not merely human exertion as a specifically harnessed natural force, but exertion as subject, which appears in the production process not in a merely natural, spontaneous form, but as an activity regulating all the forces of nature. " Grundrisse p. 611
Ted