‘The Left’ has at this point become an empty form detached from its content, a ‘floating signifier’ (just as Laclau and Mouffe wanted). There is nothing to stop various people with various intents from employing it every which way, thus fighting over the use or abandonment of the term, per se, is a chump's game. However, the term did once refer to a specific practical content, and it is this content that must be critiqued and resisted, no matter what name it goes under.
Considered in its determinate historical manifestations (the trade unions, social-democratic and Stalinist parties, Keynesian and welfarist policy advocates, 'rights' and reform movements), the Left is, as the old ultras used to say, ‘the left wing of capital.’ The Left has taken the basic presuppositions of the capitalist mode of production as givens — namely the separation of proletarians from the means of their own reproduction (whether those means are legally owned by a private firm or by the state matters not a whit to the proletarians), the existence of 'the economy' as a sphere separate from life-activity, the separation of the political from the social i.e., state from civil society, public from private, citizen from human, the regulation of access to the social store by the yardstick of labor-time, generalized production for exchange mediated by the abstract universal equivalent money, the sale of labor-power as a commodity.
The Left (at least in its heyday) set itself up within this state of affairs as a kind of tribunus plebis, promising the workers a ‘fair wage,’ a greater share of the produce of their labor. As the professional representative of one moment of the capital-relation (the commodity labor-power), the Left fought, petitioned, and haggled for labor-power to be sold at a better price, under more favorable conditions, and assumed the role of political patron of the workers-qua-sellers-of-the-commodity-labor-power (and, eventually, as the old labor movement began to reach its historical terminus, it tried to recompose its base out of other 'special interest groups:' women, people of color, etc.). It was as institutional mediator of the poles of the capital-relation that the Left, as a stratum of political specialists, rose to power to varying degrees at various times, therefore this stratum's own vested interest was to facilitate the rapid accumulation of capital, because it is only in periods of booming, profitable accumulation that there is high enough demand for labor-power that Leftist representatives are able to win concessions (i.e. better conditions, higher wages, increased working-class consumption, social welfare) from capitalists. (If the labor-market is slack and there's a huge reserve army, as there is today and will continue to be as ever more living labor is expelled from the production process, then the capitalists don't have to listen to demands from uppity unions and leftists, they can just sack the workers and hire more from the desperate surplus population. This is why you'll find Leftists today demanding the unfeasible and undesirable absurdity of full employment). Thus it is the structural imperative of the Left to stabilize capital accumulation and avert or smooth out its crises (including the 'crises' of proletarian insurrections, which Leftists have 'smoothed out' by any means necessary from recuperation to brutal repression, from the SPD in 1919 to the PCF/CGT in 1968). The means employed in this effort are almost invariably nationally-delimited and statist, even if the Left has generally only been successful in its narrow aims when it can feed vampire-like off the energy of mass social movements: the Left is their graveyard, where proletarian revolt is buried in ballots and contracts.
What such struggles over the terms of sale internal to the capital-relation have in fact achieved, historically, is to accelerate the real subsumption of labor processes under capital — if the Left succeeds in legally limiting the length of the working day, this blocks the accumulation of absolute surplus value, and forces the capitalist to intensify the labor process and introduce technological and organizational changes to increase productivity, that is, to shift to the accumulation of relative surplus value, that is, real subsumption. Similarly, if the Left succeeds in raising the price of labor-power, this adds to the pressure which the dynamic of accumulation itself exerts on the capitalist to further increase productivity so that labor-power can be expelled from the production process (workers can be sacked), and the price of consumer commodities will fall, and along with it the cost of the reproduction of the labor force.
Thus if one maintains that capital developing the forces of production, shrinking the amount of direct labor socially necessary for the reproduction of the species, and simultaneously eroding its own foundation is progressive, as we do, at least in a qualified sense (recognizing that this development has occurred only through catastrophe and mass suffering), then the Left has certainly been historically progressive. But, whatever the delusions it sometimes held about itself, the progress it has achieved is the full realization of capitalist modernity — the defeat of the old feudal/aristocratic regimes, the triumph of bourgeois democracy, and the real subsumption of labor under capital, and with it unprecedented material productivity. Its time, however, is over. With all of this long since achieved, and capital now in a permanent crisis of profitability which it attempts to attenuate by (among other things) ruthlessly contracting the social reproduction of the proletarianized class, the Left (in the historical sense elaborated here) really has no purpose except to contain and recuperate proletarian discontent in order to keep its own corpse lurching along with that of capital, as its loyal opposition.
In such a situation, Karl Marx’s admonition is truer than ever: “Instead of the conservative motto, ‘A fair day's wage for a fair day's work,’ [proletarians] ought to inscribe on their banner the revolutionary watchword, ‘Abolition of the wages system!’” Or if you prefer the words of Joseph Déjacque: “should the laborers have the produce of their labor? I do not hesitate to say: No! although I know that a multitude of workers will cry out. Look, proletarians, cry out, shout as much as you like, but then listen to me: No, it is not the product of their labors which the workers are due. It is the satisfaction of their needs, whatever the nature of those needs.”