The way I understood Blanks is not that they're necessarily soulless, but more that rather than a soul they have
something else.
Way more creepy and alien and scary.
Plus, it fits with the fact that there are different levels of Blank, similar to levels of psyker ability. For instance, the Blank equivalent to Alpha+ is Omega-.
As for emotions, it'd probably be difficult to prove whether a Blank is genuinely feeling emotion, or faking it. I think the short answer is that we don't know.
In the old fluff, the initiation right of a Harlequin was to get possessed by a daemon of Slaanesh and then exorcise it through sheer force of will. This resulted in a lot of casualties, but those who did were free of Slaanesh's pull for the rest of their lives.
Very rarely, an eldar would exorcise the daemon, but still lose their soul. Those are Solitaires. There's a couple of possible explanations for them: 1 they're eldar blanks, 2 their soul is replaced with something else entirely, 3 they steal a little of Slaanesh's power becoming in essence independent greater daemons.
If you want to have some crazy Magos/Inquisitor go down the rabbit hole making a machine that tears out people's souls to make them blanks then I say go for it

it's a big universe, stranger things have happened, and it sounds grimdark-cool which is the most important part
I think if Blanks get near daemons the daemons have more difficulty manifesting in the physical world. Asdrubael Vect has caged blanks surrounding Khaine's Gate (most likely a warp gate) to try and ward off daemons. Depends how strong they are though...