Are there any downsides to banning node crawlers?
It would be hard to specifically ban crawlers as a practical matter because there is no reliable way to differentiate them from other normal nodes. They can, in fact, just be normal nodes that instrumented with code to collect the desired data and report it back to an aggregation system.
So then you are left with banning normal nodes. Since all of the value of running a node comes from its connectivity to the P2P network via other nodes, this would not make sense.