Yeah, they develop shields, but that's still learning to control a sense. It's the equivalent of learning how to filter out other people's conversations. Eavesdropping is rude, and asking people not to do it is one thing. Asking them to cripple their sense of hearing and never take their earplugs off without express permission is different. Forgive my unqualified response to your unqualified statement; your initial argument seems to encompass everything from an emotional surface scan to a deep memory probe, and I know of no fictional universe with telepathy where those two ends of the spectrum are comparable in terms of investment and deliberation by the telepath.
If someone read my mind, they would shortly find a neverending grudge against their very existence.