If you 'want for' something, then you lack it. It's usually used in the negative, such as We were poor but we wanted for nothing. Note that we wanted for nothing does not mean the same as we wanted nothing! They may very well have wanted lots of things, but didn't need them or feel a lack of them.'If I wanted for perfection, I would never write a word' - Margaret Atwood #AcWriMo #QuoteOfTheDay #JustWrite #AcWri #WritingTip pic.twitter.com/44iN7ul1R4— PhD2Published (@PhD2Published) November 6, 2016
Want (without for) also means 'desire', however, because if you lack or need something, you may in fact also desire it, so the meanings overlap. The overlap is especially obvious if you think about a context like buying vegetables at a farmer's market. If you haven't brought your reusable bag (tut tut), the stallholder might say You'll want a bag for those. You don't specially feel a burning desire for one, but you need one, so you do also want one.
If the tweet had said 'If I wanted perfection...' then it would make a bit more sense. As it stands, Atwood seems to be saying 'If I lacked perfection, I would never write a word'. That implies that she writes because she has perfection, which is not at all the sentiment intended.
She may well be perfect, in fact - I think she's right up there in the best writers I've ever read. Top three, for sure. But it's a typo, of course... she actually said 'If I waited for perfection'.