Smart People?

Words incorrectly spelled is either a sign of mental illness or personal carelessness. A slob by any other word, spells carelessly and dresses with equal abandon.

This has nothing to do with "smart people," an undefined term. I'm pretty sure everyone has received this chain email before. I've received like three or times. Anyhow, as the paragraph suggests, "it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be in the rghit pclae. The rset can be a taotl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe."Pretty much anyone familiar with the English language could read this with relative ease. It has nothing to do with how smart someone is.

If you want people to expend effort reading what you have written, it's only polite to put effort into writing it - this includes good spelling and good grammar!

I'd hardly call the semi-sentence above as "best effort". First of all, "one" is singular. But more importantly, "thier" is actually spelled "their".
When I communicate online, I try my best to not make common mistakes. Do I make mistakes? Sure. Do I try not to? You betcha. I also try my best when I communicate verbally in real life. I try my best not to stutter, use fillers like "um" and "uh", etc. Do I sometimes stutter and use fillers? You betcha.The point is some effort is better than none.

Noone here is a monster. If best effort and politeness are both present, then we will return in kind. That said, little or no effort is neither polite nor "best effort".

No one is perfect, but does that somehow excuse the need to try?

pelican, unless you believe yourself to be endlessly fascinating, pay extra attention to #5.

OP : However, if the word is recognizable and in context, what is the big problem?

Or not understood and subsequently ignored because of crappy spelling and grammer.

Repeated spelling and grammar mistakes correlate in our heads with a lack of credibility.

If you want a technical reason look up the fundemental attribution error.

The fundamental attribution error has nothing to do with fundamentalism: it is social psychology.

A good question to ask is 'why have our brains evolved to make the fundamental attribution error?'

Most of the time some one with the spelling and grammatical capacity of a cat's arse is not going to hold much in the way of intellectual credability.

in·tel·lect (ntl-kt)
n.
1.
a. The ability to learn and reason; the capacity for knowledge and understanding.
b. The ability to think abstractly or profoundly.

It sucks when it is assumed about oneself but them's the breaks.