Twitter unquestionably deserves the online celebrations of its 10th birthday. It also deserves some big asterisks to that praise--chief among them, its failure to handle the rampant online harassment on its 300-million-strong network.

The social-media company has made a lot of changes, big and small, revolutionary and...not, in its first decade of existence: It turned stars into hearts! It flirted with destroying the fundamental brevity of its product, only to finally decide that nah, maybe that wouldn't be such a good idea. And it's currently conducting a very public sharing-economy experiment with its CEO.

That's not to undercut Twitter's serious accomplishments: Ten years into its existence, it remains relevant and often transformative. At its best, it can be the engine of social or political change. (Like so many journalists, I've watched it transform my industry and the way I work with a mixture of adoration and exasperation.) And it's so far weathering onslaughts from younger, faster-growing social-media networks--Instagram, Snapchat--though whether it can continue to do so is a subject of much debate. (It did, at least, seem to flick off Ello and Peach.)

Twitter has done most of this in the service of what seems to be its constant, lofty, and perhaps impossible goal: making itself into another Facebook. But even setting that ambition aside, Twitter has yet to figure out how to handle trolls and hate speech with anything approaching Facebook's finesse.

It pains me a little to write that line. I'm a Facebook skeptic of long standing. These days, I mostly use it to keep up on birthdays and long-distance friends' life developments (read: babies). And Twitter did follow Facebook's first-level fix for hiding people without their knowledge. (This is especially useful when relatives or former colleague start ranting about politics.)

But most importantly, on Facebook, I have to invite any authors of such posts into my life. I get to decide who can comment on my posts. Strangers can try to become my online friends, but unless I agree, they can't just show up on my Facebook posts and start telling me I'm stupid or ugly or actually, I didn't really understand the topic I've been covering for most of a decade (but they'd be happy to explain to me the error of my ways).

That all happens on Twitter. While I can prevent strangers from sending me unwanted private messages and I can punitively block them after the fact for their public comments, I can't proactively prevent them from tweeting terrible things at me. This becomes an often-excruciating problem for any woman writing online, as writers including Amanda Hess and Lindy West have chronicled. It's a problem for any woman being online; cf. Gamergate and Brianna Wu, who told The New York Times this week, "Twitter is a dark, dark place for women."

Or, to use one of the free speech analogies so beloved by the internet trolls who couch their harassment as a patriotic exercise of First Amendment rights: Twitter isn't the equivalent of the town that allows the Ku Klux Klan parade. Instead, it's become the town that posts its citizens' addresses publicly and allows KKK members to show up at their houses, to picket and yell whenever a door or window is opened, to spew their hate directly and incessantly and without restraint.

The protection from harassment is where Twitter has repeatedly failed, and where Facebook, for all its flaws, has successfully devoted a lot of time and thought. As Joshua Topolsky put it recently in The New Yorker:

If users get abusive on Facebook, they're dealt with. If someone wants to wage a campaign of noise and intrusion, the repercussions are varied and plentiful.... The fact that people have to register their real names has certainly made Facebook a much safer space in which to engage.

(This is less effective for teenagers subject to harassment from friends, classmates, and people they know, of course. But at least it's a start.)

This status quo is all the more frustrating given how many resources are at Twitter's disposal (while unprofitable, it still brought in $2.2 billion in 2015 revenue), and how much time and effort--and fanfare!--it puts into minor, cosmetic changes.

It's not an exaggeration to call Twitter one of the most transformative media companies of the past decade. If CEO Jack Dorsey and his top managers decided that Twitter's harassment was at the top of their priority list--if it was the No. 1 problem that they really needed to solve--I have no doubt that they could come up with a fix in relatively short order.

I'm far from the first to point this out, of course. To put this into historical terms: It's been 10 years since Twitter debuted, and two since Gamergate highlighted the pervasive degree to which it tolerates and enables online harassment. That's a fifth of its life, at least, that the company has spent deflecting mounting criticism over this specific bug.

So what does it tell us about Twitter that its leaders haven't yet decided that fixing its harassment problem is one of their top priorities? And at the very least, can we hope that they'll try to remove this asterisk before their 20th birthday?