I never knew that keeping cats indoors was ever a controversial take until I rescued Willow, and found out that there was this faction of cat owners who believe that cats deserve to roam the outdoors until they are tired and decide to go home on their own after a long day of hunting and/or feline fornication.
This, despite the fact that indoor cats live almost twice as long as their free-roaming counterparts. And never mind that cats, because they are still excellent hunters -- an instinct that domestication (ha!) miserably failed to completely stamp out -- are responsible for the deaths of endangered birds and small mammals.
Those who support free roaming contend that indoor cats live long but boring lives, and what kind of life is that?
This is one debate that won't die down soon. But I guess it boils down to your own personal preference. Personally, I prefer Willow to be safe, sound, and healthy inside the apartment. I try my best to keep him engaged with toys and treats and cuddles, but if he still finds that boring (but I doubt it because I had him neutered, which lessens the urge of male cats to roam), then tough luck. I'd rather have a relatively bored indoor cat than one that's flattened by a car or ravaged by feline HIV.