τοῦτο ὅ is rendered ‘as for this that.’ (1) There is no authority for this phrase used adverbially in this way: hence the conjecture τούτου, governed by τἀναντία. Otherwise we must assume an anacoluthon. (2) But CG read τοῦτο ᾧ, and quite possibly this is right. τοῦτο ἀντισχυριζόμενος ᾧ Κλέων ἰσχυρίζεται=‘while maintaining this in opposition to what C. maintains’ (cf. τοῖς ἐγκλήμασι ἀντεροῦντες I. 73). περὶ τοῦ . . ἔχοντος is then epexegetic of τοῦτο, just as ἐς τὸ λοιπὸν . . ἔσεσθαι is of ᾦ (=ἐκείνῳ ὅ). Both insist on the future, but one on τὸ ξυμφέρον, the other on τὸ καλόν.

προθεῖσι—depending on ξυμφέρον (ὑμῖν), eonditional.