First off, the "sleep" of a Mac differs from those of most other computers; Macs don't write the content of the entire RAM to the disk when you put it to sleep, it rather deactivates power supply to almost every component of the computer, except the RAM, so that, when the Mac awakes again, it never erased the RAM and kept it's content.
So it depends on what you call "bad/unhealthy", because the Mac is still powered, just not consuming as much. Meaning that Macbooks will lose battery life while sleeping, but it still may take up to weeks until it runs dry, depending on how much life the battery had when you put the Macbook to sleep.
My guess is that those "computer literate" people only knew about the sleep function of most other computers; those write the content of the RAM onto the disk when putting to sleep, and read it from the disk into the RAM when they awake. First: this may cause massive fragmentation for the disk. Second: SSDs lose life when writing on them, so this in particular may indeed be not healthy for them. Third: There is a risk of damaging the HDD while it is writing and you bump the laptop (however, this is not sleep related, and there should be technics put into the laptop to prevent this anyway).
Personally, I never really shut down my Macbook, except when I know I'm not going to use it any time soon. So again, I never shut down my Macbook, only just closing it.
Just learned that portable Macs do both by default, that is keeping the RAM powered and saving the content to disk.
So yeah, the guys told you that technically are right, but as I see it, it's as unhealthy/bad for your drive as, well, using it for anything else.