When I said "bad behavior" what I had in mind were some people who were literally trying to sell Nostr relays as free databases for custom web apps some time ago, and then some recent attempts at using NIP-32 to store events with tags like L=name, l="something" L="author" l="someone" L="date" l="2024-07-20" and then do queries using that -- the way I've seen people do makes no sense, but you could have just different tags and values without the L/l overhead and then you would query all albums released in 1973 by bands with names starting in F that have less than 6 songs with {"#s": ["f"], "#y": ["1973"], "#n": [1,2,3,4,5]}.

You get the idea: people shouldn't be doing this! And if we make it easier they will do it more, and then it will be more hassle for relays to change themselves so they can block it.

Also powerful query language means it's easy for bad actors -- or just bad-coded well-intentioned clients -- to DoS relays.