You should run a node for you, not to help the network.
A lot of people is currently running more than one node. It does not centralize the network.
You should run a node for both yourself (privacy) and to help secure the network.
It's not necessarily bad, but it could mislead the rest of the network into thinking, "oh well, we have enough nodes, I will not bother setting one myself". We want to ideally have 1 node per person (and many people running nodes), this strengthens the network. 1000000 nodes in the hands of a couple of corporations is less secure than 1000 nodes spread all over the world, by individual parties that don't know each other.
If a single person has a ton of nodes, that is a single point of failure, and you want to avoid single point of failures in decentralized networks.
That is my thinking and wanting to make sure that I was not missing anything obvious.
actually there are like 90k nodes, how many people or corporations are behind them? I hope no more than 10k.
I hope pools,exchanges, blockchain explorers and online wallets runs an high number of nodes each.
Where are you getting this information from? AFAIK only the amount of listening nodes are known and that might not even be a accurate number.