You need to leave at least 3 seconds of reaction time between you and the next car, 2 car lengths at that speed is too close for you to reliably react in time.
Also, people can't reliably judge a "car's length". It's a ridiculous measurement system, let alone travelling at 100 kmh.
Timed gap makes so much more sense and it remains mostly consistent regardless of speed. As in, you should have 3 seconds of gap regardless of if you're traveling 20 kmh or 100 kmh.
Are they talking average car length, your own cars length? One of my cars is a little over twice as long as one of the others. Timed gap truly is the better rule.
Between the customers that have refused service at my old job and all the "just rolled in" videos I've seen I just don't trust people's ability to upkeep their cars. My coworker is running around on the original tires of his 2008 Saturn and doesn't see a problem.