The Mail often gets it wrong. Who knows if they get it wrong because they're incompetent, lazy or malicious? It would be foolish to imagine we definitely know the answers to that. All we can say is that on certain stories, for example those involving race and immigration, there is a pattern of wrongness that extends beyond what you'd expect for simply incompetent reporting.
Last week, for example, Mail reporter Sue Reid accidentally/deliberately got the figures mixed up on how many migrants there were looking for work in some parts of Britain. Sure, she's the same Sue Reid who incited Polish people to break the law in return for financial gain, but you can't assume from that we know whether she's lazy, inept or simply hateful towards minorities.
Who knows why she got it wrong, but she got it wrong. And the key problem with getting things wrong is that the likes of the BNP don't care whether you've got it wrong or not; if it's something slating immigrants then they use it as propaganda. Yes, they'd have propaganda whether the Mail handed it them on a silver plate or not, but there's an authenticity, a level of trust afforded to national newspapers, which people accept - it's often assumed (rightly or wrongly) that newspapers actually check things before they go in print, and that therefore there's more legitimacy to stories that appear there rather than just being concocted by BNP members. As 5cc points out, the BNP put up Mail stories straight away - it doesn't matter whether they're accurate or misleading. It doesn't matter to them: it's just more fuel for the fire.
So when the Mail comes up with some nonsense saying that Muslims get preferential treatment to all other customers as revealed by Tabloid Watch, a lot of people will roll their eyes and know it's bollocks straight away without having to read it. But that's not the point. For newspapers and journalism in general to cling on with their fingertips to any kind of credibility whatsoever, it needs people to have some kind of ability and willingness to check things and make sure they're fair and accurate; for people to say "Look, I don't mind running a story about genuine bias towards Muslims because that would be important, but unfortunately what you've done here is misrepresent the situation. We can't run this". I get the impression - and as ever I could be very wrong - that that doesn't happen as often as you might hope at the Mail.
Getting it wrong is a bad thing. It chips away at the reputation of not just the newspaper in question but all newspapers and all journalism. Getting it wrong means that the hateful bastards who tell lie after lie after lie about other races and religions can have a veneer of respectability to mask their inherent nastiness; they can hold their hands up and say: "Not me saying this, this is a national paper telling you that Muslims get treated better in banks than the rest of us / there are more immigrants looking for jobs than locals". That's why it matters. And that's why we should care. And that's why it's a disgrace that so many people in positions of power and influence in the press don't.