system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek]What happened to the concept of anti-missile defenses by the 24th Century?

I'm talking about things like point defenses to shoot down incoming torpedoes.
gpt
It's not that missile defense systems were forgotten, just out classed by the missile tech developed to bypass the defenses. When missiles were intercepted by conventional (by 21st those century standards) weapons, missile AI was developed to randomize trajectory to varying degrees, making interception practically impossible. 

So we switched to laser tracking interception, using lasers to heat the missile, exploding the warhead before it could reach its target. This would still work on Earth, if we still fought eachother. This worked for a time on our earlier war ships, but our enemies began using more heat dampeners in their missiles. Lasers got stronger, missiles got more resistant. That is until they discovered a combination of heat dampening material with a reflective outer coating would nullify the lasers' power enough to ensure the payload could reach the target.

The only answer to that was shielding technology, which is the standard today, despite being imperfect in its incredible energy expenditures. 

Source: ex star fleet weapons engineer,  currently writing a book on human weapon evolution from the 20th century to today.