Bitcoin network follows bitcoin protocol and any message sent to bitcoin node has to follow strict rules that enforced by cryptography. If a bitcoin node has a hashing power attached to it, then it's not only verifies and relays new blocks and transactions but also creates new blocks and forces protocol rules into blockchain. So it's those bitcoin nodes that have hashing power and knowledge about protocol govern Bitcoin network and make it secure.
The basic security premises of bitcoin concept was that there would be decentralized network of bitcoin nodes each with small share of hashing power to ensure that there is no single person or small group who can control Bitcoin network. If it's not true then quite a lot of bad things could happen, here is the link with some examples of what kind of new rules can be enforced if someone have majority of hashing power under control, this is also known as soft-fork, to name a few: shorter block time interval, coin divisibility, native color coin support or require AML registration for every address and turn it into surveillance coin.
Bitcoin value comes from it's utility, it is much easier to store and transfer ownership of value by using Bitcoin network. There is a one way relationship between Bitcoin network value and amount of hashing power, the more value Bitcoin network has the more amount of hashing power would be bought by miners. But the opposite is not true, if tomorrow Bitcoin hashing power drop by two nothing bad would happen, after maximum of 2014 blocks network hashing difficulty would readjust, it would be twice easier to find a block and everything would go back to normal, bitcoin market price would not drop either.
People who create bitcoin infrastructure, provide services and innovate are those who make Bitcoin network useful and increase it's value, but via inflation hashers leech that value out of Bitcoin, in exchange they were suppose to help to enforce Bitcoin network rules in decentralized manner. That premises was broken by pools, no longer hashers have to run bitcoin software and govern Bitcoin network instead they just point their hashing power to pools and delegate their enforcement power to small group of people, and that makes that hashing power useless in terms of securing Bitcoin network.
Concerns about pools and how they erode bitcoin security were first raised more than two years ago when Deepbit acquired significant share of bitcoin hash power, but most people agreed that in case a pool would be used for nefarious actions hashers would just point to another more honest pool. The reality didn't match those expectations, Ghash.io was used for double spending. And yet two months after the incident their hashing power share was 15% bigger, and it's only dropped after they stopped accepting new hashers. This is happening because hashers do not care about Bitcoin network security and from that point of view they are evil.
Hashers are not miners, they just hash previous block looking for magic number, they don't care where this block came from or how it was created. Bitcoin network doesn't need hashers, they are parasites who are leeching value from Bitcoin without providing anything in return.
