As you said, Ralbag (and most of the commentaries) understand this to be talking about statues of some kind. (Metzudas David to 5:8 also cites this as a second explanation.) So according to that view of things, David had nothing against the blind and lame people any more than against any of the other Jebusites.
Metzudas David's first explanation (to 5:6), though, is indeed that it means people suffering from these handicaps. However, he explains the mention of them as part of the Jebusites' boast: "Our tower [this is his explanation of צנור in that verse] is so strongly fortified that even if its only remaining defenders were the blind and the lame, you would still be unable to conquer it!" So David's challenge to his men (v. 8) is: "Disprove their claim! First topple the tower while it is still defended by all of the Jebusite army, and only then deal with these insolent Jebusites - including the blind and lame people, all of whom had joined in jeering us."