I don't understand the distinction - how is a Smart TV running Roku different than a dumb TV with a Ruko box/stick attached? (I get the lifespan part of it, but lets presuming that hasn't become an issue yet)

Control. With a Smart TV, all those processes are running all the time whether you want them to or not. With a normal TV, if you don't want a device to monitor anything, you can definitively disconnect the device and it won't be able to do squat. With a Smart TV, you don't really have full control of what is running when the TV is on or not. Youtube (or any other app) could be running in the background and you don't know about it and you don't know what processes it is running. Also the voice controls (if the model support them) is always listening for it's key words if nothing else.

Is it paranoia? Maybe. Is it wrong to be a bit more cautious? Most definitely not.

If you look into SmartTV software, they have all kinds of applications (i.e. GraceNote) feeding back your viewing/surfing history and then providing you ads based on such. I prefer to not participate in their data collection and definitely don't enjoy ads, so I just disable all of that and use an STB like Apple TV that doesn't have that. Sure Apple has it's own ads, but they're far less intrusive (you only see them if you open the App Store where it suggests apps). Is Apple collecting data about me, yeah, probably...but I trust them with my data far more than pretty much any major company, and definitely more than outfits like Google, Amazon, etc. who's primary revenue stream is using your date. Or in the case of GraceNote: *selling* your data to unknown companies.