Bitcoin is designed in a way that ensures that the actors that could theoretically
harm the network are heavily incentivized to actually play by the rules.

You claim that a potential problem lies in the possibility that the big mining
pools "associate themselves". Why would the miners collude to harm Bitcoin?
If they seriously damage the trust in Bitcoin they lower the profits for future mining
and also lower the value of their infrastructure and their hardware.
Besides, a successful attack on Bitcoin would seriously damage the trust in
all cryptocurrencies. It´s not like they could just use their miners to mine
another cryptocurrency after an attack on Bitcoin.

These attack scenarios are relevant for small PoW coins (see the recent attacks
on Bitcoin Gold, Monacoin or Verge), but Bitcoin is basically
immune to this particular threat.