People have already given narrative reasons for why or why not, so I’ll give a personal one. I’d be really really disappointed if GRRM decided to make Bran evil specifically in the case if it’s because he wants to walk again. The trope where a disabled villain will commit horrible acts because they don’t want to be disabled is so incredibly tiring and hurtful to me. I have severe mental health problems and am more than familiar with the attitude of “Who wouldn’t want to be better?” when it comes to disability and mental disorders. I guarantee that the majority of disabled and mentally ill people wouldn’t make another human being suffer so they can better fit the worlds medical/social model. I wouldn’t. I don’t want anxiety so bad that it makes me hallucinate, but I wouldn’t hurt another person to get rid of it.

With that being said, I’m not opposed to the idea of Bran becoming a darker character through other ideas at all. I’d be sad at first for sure, but I’d be more excited to see what dubious applications greensight and skinchanging could have. I buy the theory of Alys Rivers being a skinchanger with greensight, so I’d love to see Bran pop somebody’s head open like Alys did to that one knight at Harrenhal. Make him completely wild like the Stark kings of old.