Never have a sentence in your paper along the lines of "the purpose of this"...You should never say something like that...
That depends on the subject. I know that in Philosophy essays you should definitely say "the purpose of this essay is..."!
I think that it's important the weigh arguments even though your trying to be persuasive. It doesn't have to be boring like:
Blah blah FOR.
Blah blah AGAINST.
If you're arguing for, I'd throw in things like:
"I shall now explore a contrasting opinion, and show why that opinion is wrong. It may be suggested that [blah blah AGAINST], but this doesn't hold water because [blah blah FOR]"
If it was me, my 3 paragraphs (obviously I don't know about the subject, so this is just guess work) would be:
1)Argument that the media needs high ratings, news papers need to get sold and so they can be expected to do what they can to make business work.
2)Set-up argument that facts are distorted, but then argue against this saying that laws are in place to make sure that what you read/see is in fact roughly true (slander/libel laws, laws stopping pure nonsense being), and so this makes up for more misleading headlines because the true does come.
3)Argument that it's okay to use people's fears to sell papers, because if people watch/read the news they can make up their on minds as to whether something is worth fearing, and if a paper/news channel promotes too much fear people will tune out knowing they've gone to far.
So I'd split my source up in that kind of way. Identify which bits fit together, and think about what people would say against your opinions.
And if it's meant to be persuasive then I guess there's all sorts of other stuff you have to do... like address the audience, use flattery and other rubbish...