TL:DR: If modern society keeps going the way it is now, it's gonna collapse because many men will no longer work more than the bare minimum to get by because they no longer have biological motivation to keep working.
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Let's take a look from purely biological/natural perspective:

Nature is construed in such a way that most beings (animals or plants) try to gather excess energy/nutrients to survive and minimize the amount of effort and thus expend as little energy as possible to survive while achieving only one goal: have kids.
We as a species have overcome this problem by dominating our environments and thus guaranteeing a food source no matter what.
This allows us to expend more energy in other pursuits and form a community, research, philosophy etc.
Most mammals are sexually dimorphic, in nature this usually means that males are bigger physically dominant over females.
Same applies to our species, males want to procreate as much as possible, females want to make sure they and their kids survive.

Now males no matter how desirable in nature have two ways to procreate:
A.) Rape the female, possibly damaging sexual organs or creating inferior specimen because of the stress on female body. Or even worse killing the female.
B.) Succeed in the mating ritual so the female picks you and you get to have consensual sex

Females will pairbond with a male because it is harder to survive alone and their kids will possibly be killed by other male.
This guarantees female and her kids that they will survive and guarantees the male access to a female willing to have more kids with him, this worked until a clearly superior mate came along who could take better care of them.


Now add society/civilization to the mix:
Society and communities were created and eventually we decided rape is really bad way to reproduce.
However, society compensated undesirable males by allowing them to earn more 'brownie points' for mating ritual.
Physical superiority could be replaced by hard work and willingness to sacrifice for society among other things.
Ingenuity and furthering the civilization were rewarded so society told women that these qualities were really good, sometimes even better than genetic/physical superiority.

Women accepted this and made it part of mating ritual, all was well and men could just work hard to get access to a willing female.
Society also told them pairbonding should be for life and their instincts are wrong (with exceptions, you know cheating etc.)
so the males they were with kept working hard to feed the whole family and keep bettering society.
This system worked fine until like 50-60 years ago when survival became trivially easy (because of increasing amounts of automation you can sit behind desk and type away and society gives you money to get access to practically infinite resources) since it became so easy women could do it, they started working and now women no longer NEED men, however they still NEED society to survive, and society NEEDS men working to survive. And if women can't work there is always the social security to keep their kids fed and healthy etc.

Now add to this increasing lifespans and globalization+population where the average number of people you meet during your lifetime goes up from a couple of thousand to tens of thousands and you get this weird situation:
Women no longer feel that they need men, so they can become more picky about the partners they're going to have kids with, the pool they get to pick from is far bigger than ever before.
A man has to compensate far more for his unatractiveness now that women can survive by themselves.
Add in the 'you go girl!' mood that permeates the media and the fact that society and allows women to fulfill their biological urges without enforcing the status quo and thus diminishing the value of 'brownie points' a man can get, ow you get a situation where men and
women no longer 'need' each other for survival.

This creates extremely picky women who only go for biologically desirable partners, which in turn promotes the natural biological laziness of the species and males who no longer have a shot at procreating start doing minimum work to survive and society slowly collapses because there isn't enough labor, no matter how hard they shame these 'manchildren' they won't work the same as a man who NEEDS to feed another 2 mouths.



Situation A:
Pre-WWI village, 300 people, 10-70 young adults who haven't been paired up yet, very low mobility.
On average, a woman had choice of 1-40 partners, she couldn't be too picky because she would most likely die if she was alone or the community would ostracize her and she didn't have much mobility(capital and services) to move to different place.
If you were (biologically) desirable/attractive son of a farmer you had no problem finding a decent partner, you kept working hard to feed them, no problem and everything's as it should be.
Now an undesirable male would do very little in nature, because he had no shot at the game and now he couldn't rape.
But thanks to society he could decide to become a merchant or a blacksmith or soldier and score 'brownie points' via a fairly important position/profession:
Merchant by becoming rich and thus ensuring survival of the woman WHILE allowing her to buy trinkets/clothes etc. to increase her social status
Blacksmith - being important part of the community, if you were farmer and the blacksmith hated you you were shit out of luck and couldn't get decent tools first hand etc., naturally this afforded blacksmiths wife a certain amount of privilege and social status.
And soldier because society told women sacrificing your life for others was seen as honor and community took care of his wife (makes no sense biologically for a woman to pick a mate who will be killed) which gave her social status.

However the last option only worked when there wasn't a shortage of men for labor in community.
So if you were an undesirable male you still had plenty of options to go for to get access to a pussy, practically speaking.

Situation B:
A small-ish modern city, 700k people, 50-400k of adults who haven't been paired up yet.
As a woman you are no longer pressured to marry and ostracized (you essentially become incognito) if you decline to do so. You have your pick of 200k-ish possible partners, you don't need a man to live and you can always just pack up and move to a different city.
As a biologically attractive male you have no problem, a little bit of effort and confidence and you get your pick. You work hard for society to keep yourself, her and your kids fed.
As biologically undesirable male you now have to perform nearly heroic acts of sacrifice for society to earn enough 'brownie points' to attract a woman.
Be it either becoming pretty fucking rich, saving a couple of kids from fire, generally becoming famous etc. and allowing the woman to gain a lot of social status by associating with you, or making yourself more desirable by working out, cosmetic fixes etc. which are both demanding and fairly expensive.

this creates a situation where all the sub 5/10s have to earn 'brownie points' to attract a partner. However earning enough 'brownie points' to succeed in mating ritual becomes fairly demanding and for some nigh impossible, this is why they decide to enter a 'vegetative state' and do minimum for society to survive.

This is how society collapses.