If you accept a ‘word’ such as ‘alright’ (which I consider to be a mistake) just because it’s in the dictionary, for consistency you will probably also have to accept ‘words’ that you consider to be mistakes. (How accepting do you feel towards nucular?)
Furthermore, if you accept any word that’s in the dictionary just because it’s in the dictionary, you are trapping yourself in an inescapable bit of circular logic.
I’m using it because it’s in the dictionary…
and it’s in the dictionary because I’m using it.
That’s because the mission of a dictionary (these days, anyway) is to document how people actually write, not to dictate how people should write.
Dictionaries are comprehensive. They’re not carved in stone and increasingly they include examples of anything and everything that’s statistically common enough to pass some minimum threshold. There’s no value judgment involved. In fact, descriptivism, the linguistic philosophy that motivates lexicographers, categorically prohibits interference from value judgments. The passing of judgment on any form of linguistic expression is termed ‘prescriptivism’ and is frowned on by academic linguists.
To my way of thinking, then, there’s a huge difference between the mission of dictionary writers and the mission of pretty much any other kind of writer. Writing is all about value judgment—writers must constantly choose what to say and how to say it to best communicate with the audience, for a given purpose, in a given context. Therefore, writers are constantly looking for and giving one another advice on appropriate forms and formulations.
There are many, many books out there that purport to contain well-considered recommendations for word use. They’re just not dictionaries.