[nl]

why get used to writing stuff wrong, when I can get used to writing them right

In that case....

"wrong" and "right" are adjectives, while "writing" is a verb which you are using the words "wrong" and "right" to modify. However, adjectives should only be used to modify nouns and pronouns, not verbs. In this case you should use an adverb:

why get used to writing stuff incorrectly, when I can get used to writing them correctly

If you prefer, you can use "writing" as a noun and continue to use "right" and "wrong":

why get used to the wrong way of writing when I can get used to the right way

I hate people who correct grammar on the internet, but you did make the mistake of asking. Sorry.

[eavc]

Those are flat adverbs, actually. :p

[thinkingisfun]

Why, I thank you! But I will also have you know that "Sorry." is a sentence fragment. When correcting others, you should always try to correct them rightly, not wrongly, even if it may sound odd sometimes.

(tee-hee :)

[eavc]

In case you intended to take that advice to heart, you can use 'right' and 'wrong' as adverbs in all but the most formal contexts, and possibly even then too. They're called 'flat adverbs,' and there's a great video post from MW that you can find if you Google the term.