Yes, I know that you do not see anything wrong with that picture. The top 6 companies have 60% of the hashrate. What could possibly go wrong? As long as there is sand around...
Yes, but you would be saying the same thing if it were 10 with 60% or 20 with 60%. These are pools, miners can re-direct their rigs anytime. They are not going to conspire to destroy BTC, what would be the point.
exactly right. if Bitcoin becomes a mainstream currency, mining pools have a chance to become the accountants of the entire system which would mean enormous profits. but if they attack themselves, they get nothing.