I don't think that fund investors were "dumb", just greedy and aware that corporations rule. So why worry about risk? Governments, that is, working people will always pay for any damages the corporations cause, notwithstanding Obama's assurances that BP will pay for everything. While corporations like BP are too big to fail (see this), American workers are dispensable.
...whenever greens or ethical investors warned them about BP’s cavalier behaviour, instead of thanking them, the big fund managers reacted with hostility. On 15 April, five days before the Deepwater Horizon explosion, a group of investors led by Co-operative Asset Management tabled a resolution at BP’s AGM requesting more disclosure of the risks it was running in its tar sands operations(12). It was one of the most successful ethical resolutions ever, but all that means is that funds holding 15% of the shares either supported it or abstained. The other 85% supported the company’s right to keep bamboozling them.