This is fundamentally the problem with Labour at the moment (and indeed the piece). Labour historically had been a broad church of people with a broad understanding that compromise and sometimes "holding your nose" over something in exchange for the greater good is necessary for the common goal of making things better for not just the poor, but everyone.
As Marckee says, somewhere between 97 and 2015 something got lost along the way - the party in it's New Labour guise did much that was good (minimum wage, NHS/education funding), and brought in support from new areas, but forgot to continue conversing with the base that allowed them to do that. I don't have the exact answers as to why, but there's a reason that the BNP and then UKIP grew from negligible support to 12+% and the broad coalition splintered with increasing numbers voting for previously insignificant parties.
The trouble is that on the one hand, the centre-left/moderates within Labour don't seem willing to address those issues, while the further-left/Corbyn supporting part of the party is - as @asita has often said - unequipped for leadership. As I've said many a time on here, how it gets resolved in the medium term is beyond me. Both sides are vying for sole control of the party at the moment rather than working together for the betterment of the common cause (I choose not to ascribe blame either way in this post for that it's utterly irrelevant to the fundamental point) and I don't see either backing down anytime soon.