Based on the tenuous assumption that anybody can read any thoughts of anybody else and that there's no way to hide them? Telepathy is just psychic communication. There's no reason to believe that a telepathic species can't hide information from each other, any more than any other random species. Them being some sort of phychic hivemind with no sense of individuality is NOT supported by any evidence.Thing is, how do you get away with something like that if everyone is telepathic? Among themselves, they could be perfectly, utterly law abiding because it's literally impossible to get away with anything.
Granting your assumption, have there never been any conflicts on their worlds? Does everybody-can-read-everybody's thoughts mean that individual nation states can't form and fight for resources? Does it mean that they have never and can never encounter any other technologically comparable foes that might try such an attack, or they try such an attack on them? Indeed, they obviously can and do think of ways to blow shit up and defeat enemies, so them not ever considering electronic warfare is STILL stupid.