It's much easier to establish a psychic channel with a member of another psychic species. We generally go to great effort to maintain mental walls to keep them out, however. Most of our basic telepathic training involves learning how to defend our minds, isolate them from the outside world so that we don't project our thoughts on others and so that other telepaths can't easily invade our thoughts.

There's a legend that a very long time ago, long before Time Lord civilization, there was an era where Gallifreyans communicated primarily through telepathy and that at times it almost bore a resemblance to a group consciousness. But these days we keep our minds to ourselves, and vigorously protect our mental space.