a) Witnessing the havoc Accenture consulting unleashed upon a couple of businesses personally b) Knowing, albeit superficially, a load of people who currently work or had worked at Accenture. With the exception of one they're the poster jerks nobody likes.
Edit: I hate to suggest it, but perhaps there's also a bit of a perceptive bias going on, in both directions. I look for the good in people, and I found plenty of awesome people in Accenture. If you expect Accenture people to be arrogant idiots, probably every Accenture person you meet will look like just that.
FYI, they cancelled one of the twice-yearly promotion points because of the NHS debacle (which resulted, iirc, in a $450m write-off by Accenture UK, and basically wiped out the profits for the year). That pissed off a lot of people and caused a lot of their best people to leave the company. So, yeah, they took a big hit!
It still amazes me how many major disasters these large firms can absorb. A 450mil write-off would cripple most businesses. Not picking at Accenture specifically but I've seen Cap, IBM, etc all get doused by law suits and/or write-offs that are absolutely massive.
When Accenture finally caved and gave up, the share price increased significantly.
Either way, Accenture has an awful reputation within the technology sector imo.
On the other hand it took GM decades to burn through their reputation until they had none to salvage. Now they apologize profusely for being a shitty car manufacturer. I still won't buy one btw.