The reality is singlespeeds, like for like when it comes to rider input are slow up, slow down, slow on the flat.
Like for like on rider input then they are faster uphill as they are lighter.
However the main point is that they are more FUN and weirdly addictive.
They make you work harder over the ride, which is a good thing if you are a time-poor middleaged bloke...like me.
Rubbish. If they are like for like
, e.g. same weight they will be slower in all but exceptional circumstances. The same effort applied to selectable gearing will be faster around a given course if the terrain has any variety, there is no doubt. Mountain biking didn't just adopt gears for marketing.
Work harder on your geared bike, same difference, its a cop-out to say its only something a singlespeed can provide.
BIKES are fun and weirdly addictive. Its got SFA to do with the gears.
People make these things up as justifications to cloud the reality that they're just hopping the alternative bandwagon because they think its cool, or they just want to try something different. Nothing wrong with that! ...But making stuff up like its better because its more difficult (why did we ever progress past 50lb coaster brake beach cruisers then?), it makes you faster because you try harder (of course you go faster when you put in more effort!), or rigid forks make you a better rider (pick better lines on a technologically advanced bike and see what happens!), is just self-deception bordering on ego stroking.