What does a tonearm contribute to the sound of a turntable?

In a perfect world a tone arm contributes nothing to the sound. It just allows the cartridge to track the record and convert mechanical squiggles into electrical impulses. Practically it adds distortions. The better ones add less than the mediocre ones. 

I still don't understand the fascination of using vinyl.  Unless people love the sound of noise caused by tracking on a groove.  Noting like the sound of noise when hearing music.  Streaming music is now the future.  Quit buying expensive records and turn tables and realize your turntable is headed for the museum.  You don't see phonographs anymore.  Who wants to get off the sofa, take a vinyl record off the turntable, find a new one to listen to it, clean the record and get another record started when you can sit on your seat and select a huge selection of music by using your cell phone to do so.  The money you spend on a turntable and records could be spent on upgrading your speakers and amplifiers.

Larry, Larry, Larry. You must be a millennial. 
I say spend as much as you can on vinyl playback and upgrade your amp and speakers too!  😉

@larry5729.   Nice ironic post illustrating the short-sightedness and lack of audio depth of much of the younger population. You perfectly illustrated how a certain segment of the listening population just isn't deep enough to appreciate vinyl.  Well done.

Don’t get sidetracked into a Vinyl vs Digital vs Tape debate... that was not the OP ?

actually you can pick a low resonance arm/cartridge system ( and they are indeed a system and yes compliance and mass matter ) by listening with no volume....

Great bearings that last and stay great for the lifecycle of the arm are imo essential.

OP that FT-3 is no slouch, let me know IF it needs a home. On a SOTA Sapphire it can be formidable, but that’s another thread..,