It’s not the reason why most people learn, but for those that are interested in that aspect, Tai Chi has a range of effective methods for keeping you safe.
Tai Chi is not great for sport fighting, you see it being used for that, from time-to-time, but it generally looks indistinguishable from wrestling. However, when it is used for self defence it’s quite different and generally both looks – and is – quite dangerous.
Most of the moves in Tai Chi were created hundreds of years ago in China and there, the idea was almost certainly to make sure than an attacker could not come back and try to attack you again. A lot of the defensive moves cripple or even kill an attacker. Which is very far from what Tai Chi has come to symbolise when you think of elderly people moving slowly and looking serene.
Tai Chi, as I have said before, is a very deep art and some people are interested in learning and practicing the self defence aspects. Other people are not interested in self defence and that is OK. As has been mentioned before, Tai Chi is very accommodating and once you start to practice it, it becomes your art.