I think we need to be a little more specific here. Using talk text or l33t does not inhibit my ability to write a logical, mature and well punctuated sentence. The difficulty that arises is the ability of other users to interpret the words in their correct, unaltered form. It is pehaps, the Western world's version of Kanji. That is, the use of smaller symbols or groups of characters to indicate a larger word. However, many of us don't appear to be too appreciative of our simplification, mostly likely because it is not well uniformed or studied.
Qu!+3 phr@n|<1y, 1 d0n'+ <@r3 1f 73h 53n+3n<3 15 wr!++3n 1n 733+. IAY on'tday enevay arecay ifay itay isay rittenway inay igpay atinlay! However, I do care if the post that I am reading consists entirely of three words and doesn't really have any great contribution to the topic at hand. I also believe that if people are going to write in plain English, they should at least bother with capital letters, full stops and commas where required. Getting the correct word for the meaning would also be nice. "I no there is one" v. "I know there is one".
I don't expect that everyone writes everything perfectly. Heck, there are probably a number of mistakes in what I have written already however, a little effort and pride in one's posts can make a huge impression and collectively will determine the quality of a forum.
Difficulty in interpreting l337 is only increased because everyone has a unique style.
+h1s 15 |337, b|_|+ +H3n 4641n,
50 15 +1-1|5. 7|-|15 |\/|33|\|Z 1nt312p12371n6 07|-|3125' 1337 |(4|\| 133 1|\|73123571||\|6 |3|_|7 (|-|4|_|_3|\|61|\|g.
However, as you said, you can form complete sentences using it. Not only that, but because you are forced to think about what you are reading (and what you are writing) as you interpret it (and write it), the meaning of the phrase comes out as you mull over what you are reading your head. It's like typing in bold, but better.
dis is hrd 2 red do lol adn looks lyk u r tryin 2 jos b00st ur potsst cont by typin lotsa porly typd mesages adn uzully thes mesagis ususlay cotanz an incoherint mesage. Although reading such messages also forces you to think about what you are reading, the WRITER doesn't have to think while typing it, so usually the message contained is not relevant or well thought out.
But when it call comes down to it, you can't stop people from typing in leet just 'cause they think it's cool, and you can't stop people who type in txt tlk just 'cause they are too lazy to fully type out messages.
Have you ever considered how "txt tlkers" feel when they speak to someone who types and speaks properly? They probably think that people who do so are pretty condescending.
You can't stop it, mostly because you can't make everyone happy.
Best you can do is learn to live with it.