I saw it all (big Corrie fan) - yes, Sean was negative, and said he couldn't wait until Violet stopped breastfeeding so he could have a bigger role.
His boyfriend, the midwife, challenged him for not being very PC, and there was some brief discussion about the propriety of 'flipping them out in public' which Lauren joined in with.
But I thought the vibe of the scene was that Sean was being a dickhead, really - it was a stupid thing to say, but in line with what Sean feels about the way Violet and Jamie are excluding him, and character-led, too. This is what Sean would think - he acknowledged he wanted the baby to grow up 'brainy' but also acknowledged his resentment at the fact he could not be hands-on with feeding.
So, all in all, I think it was positive about breastfeeding as the only people who said anything negative are people who we are clearly meant to think of as a bit pathetic and needy (Sean) or daft as a brush and shallow (Lauren).
Marcus the midwife could have been a bit more vocal about defending it, though. OTOH, there are plenty of midwives who are ambivalent about bf