Barcelona are bigger and superior club to Arsenal, it then stands to reason he'd have to be better to get into their first team, which he very probably would've done over time. I don't see how you can hold that against them in this instance.
They, like us, would obviously have a time frame for each of their academy players to come into fruition for their 1st team squad, Arsenal came in and completely fecked that and even though it was legally OK, there was clear moral outrage from Barcelona at the time for what they saw as a completely underhanded practice. Now it's Arsenal's turn to be on the end of what they see as completely immoral behaviour, and they don't like it.
Those may be the cold, hard facts, but in reality, there will be a lot of emotion and negative undercurrent to this whole saga.
Barcelona will feel sick if they have to pay top dollar for their own player, and rightfully so.
As soon as Arsenal took Fabregas against Barcelona's will, all fair-minded or conscionable scruples went out the window.