That doesn't sound like a solid indicator of an issue. Two friends could be having a back and forth discussion with no harassment or conflict. You'd end up with 25+ replies and 1 like.
I doubt it's because they can't. The more likely answer is they don't want to.
Your assumption that people more intelligent than you "should have figured this out by now" belies the very problem- no one has yet come up with a good automated solution for this. If YOU do, you'll be a millionaire.
People have become millionaires, billionaires even, for the exact opposite of what you say. You become rich by making sure controversial content is spread as far and wide as possible, because hatred and fear sell as entertainment. People get addicted to it. You don't become rich by filtering out hateful content, you become rich by enabling it and spreading it because that's what people want (as long as they're not the target).
The real problem is the incentives, both for Twitter and for people interacting on twitter. The solution is probably _social_ rather than technical, but as long as Twitter wants to keep your eyeballs on their site for as long as possible (so they can sell ads or whatever to advertisers) a whole host of solutions are going to be verboten.
By way of example, Hackernews literally has a feature to just lock you out of the site if you are using it more than you want to. That is great for us, the users. But twitter would never do such a thing.
This is not an easy problem, and it does no one any good to pretend that it is. Tackling the issue also requires those considering it to consider other social situations. Is someone supporting equal treatment of women in Saudia Arabia practicing hate speech against the conservative ruling party? If we'd had systems that let us actively regulate speech in the way we can now, would it have been appropriate to block Martin Luther King Jr. because his message was growing civil disobedience and causing families to bicker over race politics? Why are we so damn certain that any argument today will necessarily be decided by a regression rather than a wider acceptance of more progress? Change in human societies is always ugly, always comes at the cost of pain and strife, and on the balance has usually moved us in a forward direction. I can't say the same for censorship. Censorship makes impossible any forward movement, and only serves to leave regressive mindsets to fester and make-believe that they have more support than they actually do.
I see these people here trying to debate solutions like good engineers, but unless they work at Twitter, it's a waste. We can guess all day and come up with a million solutions but when it comes down to it, Twitter absolutely has the ability to control posts that spiral out of control. What they don't have is the desire to do so.
I was about to argue against this but then realised its worse than you suggest.
If I as a white person used the N word to describe a black person I would be labelled a racist, whereas a black person can say it all day long. But even if I black up and say it, its even worse. But then with gender the rules are almost reversed, I can declare myself a woman and expect that to be somewhat respected.
And on the internet no one knows you're a dog, or a transvestite in black face.
All while "learn to code" is used to harass in some contexts...
But we expect twitter folks to just figure out an algorithm to filter out "hateful" posts, when there isn't even an accepted definition of hateful? The first replies it would filter is all the people telling Trump how bad and evil he and his policies are, while the people who try to actually harass people will find quick and easy ways to game the system, as they always have; that's my prediction of a 'best' case outcome.
I don't use the like feature on the website at all and often comment on artwork saying how nice it is or whatever.
Not always, but often.