It boils down (others said it before me) to
- 8/8 means that there will be significantly more “kicking out of disagreeing nodes”
- The disagreeing node may disagree correctly, so kicking it out is wrong
- Time to consensus, on average, will increase because of the increased cases of not coming to consensus and having to reform the group
- Avenue of attack increases, especially disruption of the network
The attack vectors is as important as the reduce ability to reach consensus and to detect incorrect consensus.
The first attack I thought of when you require 100% consensus is one of a botnet, or even large groups which decide they want to disrupt the SAFE network. The mobilise large number of PCs to get themselves as part of a large number of groups, then deliberately disagree. Then the network is unable to work efficiently. If done with enough and often enough then the network may begin to have noticeable issues. remember that one PC can have multiple nodes, so a few hundred PCs can cause a lot of groups to be disrupted.
When the network is of a large size the following is reasonable to happen
When you have 28/32 consensus this does not happen because it is extremely difficult for any large group to get 5 nodes in any one group let alone in enough to be noticeable. Even 10,000 or 100,000 nodes controlled will see it difficult to disrupt even 1 node in a decent sized network
But when you only need one node in a group to disrupt it then huge problems and the attackers can simply get more groups controlled simply because of the number of nodes and only needing one node per group. 100 nodes can disrupt 100 groups, 10,000 will disrupt 10,000 nodes and so on