Why does it need lots of full (non-mining) nodes? Unless you are mining, adding a node to the system just adds network traffic for little benefit. More full no

Why does it need lots of full (non-mining) nodes? Unless you are mining, adding a node to the system just adds network traffic for little benefit. More full nodes don't provide a better service for bit coin, nor do they provide better security. (If your full node spots a double-spend, so will everyone else). It is just duplicating work that is being done elsewhere. Sure, if you really want to analyse all the blockchain, go ahead and run a full node, but IMO it's ridiculous to want to add incentives for people to do this. People talk about how running a full node improves decentralization, but they don't prevent any extra attacks on the currency. If there was/is a worrying concentration of mining power, that is a problem, but adding more non-mining nodes does nothing to alter this.