We should be clear: before I point out that this claim has no basis, the Mail basically does that itself by using the phrases 'it is claimed' and 'research shows', but never actually saying who claims it or what research it was. The Telegraph is even worse, repeating the story by quoting the Daily Mail, and saying 'experts believe'. All of this is clear indication that the journalist or some news/publicist person has made it up.
Let's begin. Citing Twitter and Facebook as being the culprits of degrading young people's language is dubious to start with. Young people use other types of online communication far more than these largely adult media. What you mean is 'whatever online communication young people use these days'.
Using 'terser sentences' or being 'curt' may well make a person appear 'aggressive'. But what are the measures by which these girls' speech is being judged as 'terser' or 'curt'? Shorter, maybe? Than what?
Marie Clair says this:
To any outsider, there aren’t those pleasantries that there were when you wrote a letter to someone.
No - because we've all worked out that it's a bit daft writing 'yours sincerely' in a facebook comment. It's all about register. If these girls don't know how to write a letter properly, well, that's another problem and one that should be addressed, but it's not Twitter's fault.
Apparently girls 'communicate more than males'. Well, I've no idea if that's true. Seems like one of those claims that doesn't really stand up, but maybe it's true. Let's give her the benefit of the doubt and say it is. (Still doesn't excuse the use of 'males' when she means 'boys'. They're not animals.) But I think 'Deborah Cameron, professor of language and communication at the University of Oxford' (gasp! they asked an expert!) is more likely to be right when she says, in a different part of the article,
The teenage years are a period of life where you find linguistic innovations of all kinds, and girls are generally ahead of the curve. People often put down as ‘girls’ language’ something that’s actually going to spread through the whole speech community.
The article also says this:
Professor Cameron said it could be right that teenagers’ language styles in general are getting more aggressive, however there is no ‘hard evidence’ of this at present. Hard-core swearing is still most associated with adolescent and young adult, working class males.
So what she basically said was 'no, there is no evidence for this claim'. Which actually entirely contradicts the whole message of the article, but what the hell, let's include it anyway - no one will notice (and actually the commenters don't notice).
Anyway, let's all calm down with this article which says that there is no evidence that texting harms spelling, and might even be good for it, and this one in which Carol Ann Duffy says texting is good for poetry.