In light of the 'Bois Locker Room' incident which came to pass recently, a lot of allied issues arose, one being the propriety of #MenAreTrash. In this context, we came across the this tweet:

Below is a compilation of arguments in favour of the idea (taken from three articles: Link 1 | Link 2 | Link 3). Would be great to have a discussion on this with everyone, so please feel free to expand.
First things first, women KNOW that not all men are trash. The hashtag and semi-social movement "Not All Men" wants us to know one thing - good men exist. And surprisingly we know that. Wonderful men exist all around us in fact, we are friends with them, we are in love with some of them and we were even raised by some of them - so we really do recognize that great men exist.
But the phrase "men are trash" has nothing to do with those men. It's best explained by Jesse Vhasy Rasoesoe using a simple snake metaphor -
"We all know that snakes are dangerous, yet there are some snakes which are not deadly at all. However, you never hear people say ‘some snakes are dangerous, some are not’. They just say, ‘snakes are dangerous’ because it is hard for the average person to tell which snakes are dangerous and which snakes are not, so they urge people to be cautious of all snakes."
A general point of contention has been that "men are trash" and "boys will be boys" has overlapping tones. Which basically means that saying the phrase "men are trash" is just lowering the expectations we have from men - essentially saying that men have always been a certain way so if they do act in accordance to that standard there's no surprise.
So should we stop saying "men are trash" - I don't really know. It's a confusing web to undo. I don't think the phrase "boys will be boys" has the same implication as "men are trash”. The first phrase simply excuses men for toxic masculinity and the latter is more of a jolt - a rude, almost derogatory shake that men should do better and phase out the saying.
When it comes to the argument that we should stop saying the phrase because it's generalization or untrue and has hurt the sentiments of many men - I think we should let it stay. The whole idea of the phrase is to bolt the receiving audience, to be a little rude and unapologetic so there's some form of reform. Another factor is that the phrase is a form of solidarity of the frustration and tire of women around the world - and we should let it stay that way because it's the one coping mechanism we have learnt to battle our everyday struggles with toxic masculinity.
Regardless, it’s troubling to have to tackle the “not all men” objection every time we try to critique masculinity. It puts the spotlight on men who aren’t a problem, rather than men who are, and serves as a distraction tactic which derails and trivialises the original grievance. Imagine we are talking about a spate of road traffic accidents, and it is noted that “people are driving too fast.” It would be strange and unhelpful to respond with “not all people are driving too fast!” It misses the point.
Yet why not instead say “some men are trash”? First, because it doesn’t preserve the meaning of “men are trash.” Some people are trash, that goes without saying, from which it follows that some men are trash, some women are trash, and some non-binary people are trash. “Men are trash” is more informative: it picks out a particular correlation between masculinity and trashness.
More importantly, complaining that “not all men are trash” isn’t a real challenge, because “men are trash” doesn’t mean “all men are trash.” Philosophers call the former a “generic” and the second a “universally quantified statement,” and they express different things. (A related mistake is made by those who choose to interpret “Black Lives Matter” as implying that no other lives matter. In both cases, the “error” seems wilful and malevolent.) Generics are generalisations where the number of cases isn’t specified, but the correlation is important. Consider the uncontroversial statement: “ticks carry Lyme disease.” Only around 1 per cent of ticks are in fact carriers, but we accept this generalisation because it’s helpful in reminding us to be careful of ticks.
In this way, generics can act as warnings.
Further, the things “men are trash” tends to criticize—entitlement, forcefulness, failures of empathy—have not held men back. Contrast this with “women are irrational,” which feeds a baseless stereotype that continues to limit women. On the contrary, “men are trash” combats hate; its target is misogyny. And if we cry “hate speech” every time an oppressed group condemns the ways in which a privileged group treats them, we will miss vital opportunities to disrupt harmful power dynamics.
Yet I see a lot more men defending the actions of other men than those joining in to support women. These men are quick to criticize the generalization yet do nothing to stop men tarnishing their reputation. I think if your outrage & discomfort only comes when you read generalizations like “yes all men” or “men are trash”, then your priorities are wrong. And your outrage is only for an issue that you are the beneficiary of, and you are not ready to see your privilege being threatened.
I'd attempt to distinguish the example that you've introduced. The idea behind the movement is that almost every woman has experienced some form of sexual harassment from some man at some point in their life. The fact that it is so rampant/under-reported/accepted as a fact-of-life distinguishes 'Men are Trash' from 'Muslims are Terrorists', where in the latter case we know that the phrase would demonise a religion for the actions of a few extreme zealots who take to terrorism.