Liberals have always emphasized the need for collective action

With its narrow focus on class conflict, Socialists are less likely to understand collective action than liberals.

The first "speech" that is usually seen as the "birth of liberalism" is the "Oration Of Pericles" delivered by Pericles in 431 BC, in which he emphasizes the need for collective action against Sparta, and he emphasized the uniquely free lifestyle of the people of Athens, and the risk that it could all be lost. From Wikipedia:

"If we look to the laws, they afford equal justice to all in their private differences...if a man is able to serve the state, he is not hindered by the obscurity of his condition. The freedom we enjoy in our government extends also to our ordinary life. There, far from exercising a jealous surveillance over each other, we do not feel called upon to be angry with our neighbour for doing what he likes..."^[15] These lines form the roots of the famous phrase "equal justice under law." The liberality of which Pericles spoke also extended to Athens' foreign policy: "We throw open our city to the world, and never by alien acts exclude foreigners from any opportunity of learning or observing, although the eyes of an enemy may occasionally profit by our liberality ..."^[16] Yet Athens's values of equality and openness do not, according to Pericles, hinder Athens' greatness, indeed, they enhance it, "...advancement in public life falls to reputations for capacity, class considerations not being allowed to interfere with merit...our ordinary citizens, though occupied with the pursuits of industry, are still fair judges of public matters...at Athens we live exactly as we please, and yet are just as ready to encounter every legitimate danger."^[17]

This speech is considered the embryonic beginning of the liberal tradition in the West, at least in written form.

But consider how some people speak of Socialism:

Liberals have, for centuries, argued that the current system can't be fixed by individuals in isolation, that people must come together to solve their problems, and that Socialism is bad because it keeps people from working together. I'm thinking in particular "Democracy In America," by Alexis de Tocqueville, which was published in 1835, and which is full of quotes about the urgent need to work together. For instance:

"In democratic countries the science of association is the mother of science; the progress of all the rest depends upon the progress it has made."

and also:

“The most democratic country on the face of the earth is that in which men have, in our time, carried to the highest perfection the art of pursuing in common the object of their common desires and have applied this new science to the greatest number of purposes.”

Tocqueville was too early to address the issue of Socialism, but later writers in the liberal tradition have made the case that centralizing the issue of class will tend to alienate those who primary orientations toward society are seen through a prism of religion, gender, race, or a hundred other personal attributes.

Of more recent liberal writers who probably put the case most directly, consider The Moral Basis of a Backward Society, By Edward C. Banfield, Copyright © 1958:

"Most of the people of the world live and die without ever achieving membership in a community larger than the family or tribe. Except in Europe and America, the concerting of behavior in political associations and corporate organization is a rare and recent thing. Lack of such association is a very important limiting factor in the way of economic development in most of the world. Except as people can create and maintain corporate organization, they cannot have a modern economy. To put the matter positively: the higher the level of living to be attained, the greater the need for organization. Inability to maintain organization is also a barrier to political progress. Successful self-government depends, among other things, upon the possibility of concerting the behavior of large numbers of people in matters of public concern. The same factors that stand in the way of effective association for economic ends stand in the way of association for political ones too."

Banfield argues that the success of any society is measured entirely by the ability of the people to come together and work in a united way towards shared goals. Banfield was a "conservative" who served in the Nixon Administration in the 1960s and 1970s, but he also wrote as part of the liberal tradition.

If you seriously think that liberals have not emphasized the need for collective action then you have no understanding of the liberal tradition. Liberals have been emphasizing the need for collective action for at least 2,400 years.