Why is the current Left so dominant and powerful?

Why is the current Left (i.e. the post mid-1960s New Left) so dominant and powerful? 

Since the mid-1960s the mainstream Left has transformed from its Old Left roots in communism and socialism, based on transformations of economic and social structures; to the new Left rooted in multiple, additive and fluid oppositions - anti-racism, feminism (anti-men), environmentalism (anti-CO2). 

And throughout by the many-faceted sexual revolution evolving through anti-family, anti-monogamy, anti-marriage, anti biological sex and sexuality, and now pan-societal chosen subfertility and extinction.   

How and why did this New Leftism swiftly so universally dominant that it overcame more than a century of Old Left socialism/ communism; and the New Left now includes and embraces all its mainstream would-be opposition ideologies such as Republican, Conservative, Libertarian, Nationalist* - even theocratic etc? 

This is an important question because so many who oppose the Left try to emulate and exceed the Left's power by studying and copying its methods. 

The reason for the pervasive, continuing, and (so far) unstoppable domination of the New Left is very simple. 

1. New Left is essentially oppositional. 

2. New Left is therefore essentially destructive, not constructive. 

3. It is much, much easier to destroy than to construct.

The weakness of the Old Left was that it was partially constructive, indeed utopian - the communists and socialists all had a (more or less detailed) picture of some kind of future and stable ideal society towards which they purported to be working. 

For example, a core ideology of the Old Left was economic equality - aiming therefore at a very highly equal "distribution" of income (especially), and also wealth (to vary degrees). 

(But not power! The Old Left invariably centralized power, so that the revolutionary class could control everybody else for their own good!) 

Another core objective of the Old Left was the imposition of public ownership of the means of production, usually by some version of nationalization or worker-control.  

The New Left has long-since abandoned any such constructive notions: there is no ideal future society being aimed-at, no utopia.

Because it has all-but abandoned even the intent, even the pretence, of construction; it is therefore very easy for the New Left to change society by opposing and destroying whatever it currently deems to be bad. 

Destructive change is vastly easier than constructive change, and when New Left is aimed-at a wide (and expanding) range of destructive changes; then destructive change of any thing the Lefts deems bad is perceived as an effective exercise of Left power. 

*There is no such thing as The Right in modern mainstream politics. All parties and organizations are now of-the-Left. This includes churches. 

In conclusion; the New Left is so powerful and has come to dominate the entirety of high-level institutional life in the West because it seeks and achieves destructive change; and destruction is quick and facile compared with construction. 

And this is, of course, why those who desire to oppose the Left cannot use the methods of the Left

...Because using the methods of the New Left is necessarily to pursue the agenda of the New Left.