I must say that bad spelling and grammar are a pet hate of mine. I'm not saying it has to be perfect, but being easy to read is definitely preferable.
Someone asked why it should matter, as long as you can understand it? That depends on how much effort needs to be put in to undertand it. Written communication should put the onus of effort fully on the writers side. The reader shouldn't need to make any effort if the writer has done their job correctly. The reason it matters is because as soon as you start not being bothered it means standards slip and they then continue to slip further towards non-existent. This is the root of the issue we see already, schools are not enforcing those standards and work doesn't get marked down for errors. If there is no detriment then why should anyone make the effort to be correct?
What if we applied that logic to other areas? Let's say not to bother if you get charged the right amount in a shop, whether you get correct change, whether your employer pays you correctly, whether your taxi/train turns up on time. Where does it stop?
People obviously know they 'cannot spell' but that is mostly a cop out for 'I can't be bothered'. As someone else pointed out, many claiming to be dyslexic have no problem spelling it but can't spell other words. As Robbo pointed out, paintball must be a sport that attracts dyslexics as we seem to have a lot claiming this. There are people that genuinely suffer from this affliction and to have it being used as a general excuse is awful.
If a red line appears under a word then you can click and have it corrected. Then learn which words you spell wrong and make that tiny bit of effort to get it right next time. If you learn to spell one of those awkward words a day then you'll improve dramatically in a month.
The most awful thing is when errors creep in to things like official letters and signs, as per another example above. Good written and oral communication will always be a big factor in one persons initial assessment of another's intelligence. That's just human nature, as there is usually a general correlation between the two.
