[rutthenut]

It isn't illegal everywhere.

Acceleration is a big part of the enjoyment of fast cars. That's not usually illegal.

Also, having better acceleration can help reduce the 'time exposed to danger' when overtaking, which may still be below the local speed limit. Faster cars can be safer, see...

[andylynch]

You may be conflating acceleration with velocity?

Acceleration is definitely helpful (to a point , even on the track), but for instance I live in the UK where the max speed limit is 70mph, and my very ordinary car is specced to do more than double that. I don’t see the benefit of being about to do >>100mph outweighing the risks- earlier comment mentions how this arises from the need for useful torque bands in IC engines which explains a lot and makes perfect sense, but with modern engine controllers and especially electric I agree that this is no longer necessary to leave enabled in the vast majority of vehicles.

[sawjet]

Can your very ordinary car maintain that top speed at a maximum duty cycle without overheating or causing unnecessary wear to the engine or drivetrain? Have you ever actually used your car at its limits? It's not something that you would want to do for long periods of time. Now imagine your cars limit is 70mph.

[andylynch]

No but this is why you would use a speed limiter rather than changing the engine. This is already done on every HGV in the country and most mopeds.