Horses like to ridden. They have a good
life and enjoy running race tracks.
The best life would be to not have humans on their backs.
Horses generally have to be broken in before they can be ridden. To say they like to be ridden is an assumption, lets just not ride them in case they don't want to be ridden.
Many horses lose their lives on race tracks. And there is lots of footage on youtube of horses not wanting to run at all.
Just get a bike instead.
Here is a great video that explains the cruelty in horse riding.