A central belief of contemporary capitalism is that the labour of the worker is a commodity like any other in search of a buyer.
“Apologetic economists… say:… [the worker’s] labour-power, then, represents his capital in commodity-form, which yields him a continuous revenue. Labour-power is indeed his property (ever self-renewing, reproductive), not his capital. It is the only commodity which he can and must sell continually in order to live, and which acts as capital (variable) only in the hands of the buyer, the capitalist. The fact that a man is continually compelled to sell his labour-power, i.e., himself, to another man proves, according to those economists, that he is a capitalist, because he constantly has “commodities” (himself) for sale. In that sense a slave is also a capitalist, although he is sold by another once and for all as a commodity; for it is in the nature of this commodity, a labouring slave, that its buyer does not only make it work anew every day, but also provides it with the means of subsistence that enable it to work ever anew.” ―Karl Marx, Capital Vol. 2, Chapter 20 section 10
I’m not sure it’s actually a central tenet of capitalism therefore.
But think how fucked we’re getting if Guardian letter writers aren’t even getting Marx right?