Correct... there are more important issues we could be concerned with than something as superficial as "does this minifigure look happy enough?" Most actions figures don't smile, so it's not like LEGO is skirting some kind of line compared to other toys.
I'm sure minifigs do look more serious now than they used to, though I suspect the author's view on how
much more conflict-oriented the themes are now is overstated. Maybe my frame of reference for what "older set" means differs too much from his... but I'd call Cowboys vs. Indians or Pirates vs. Sailors "conflict-oriented" themes, and they've been around at least since I started playing with plastic bricks.
Of the few non-themed sets I've bought recently, here's
an obviously conflict-themed one (police vs. robbers) and everyone is smiling. If this is a consistent trend, I don't see much reason to think this is "minifigs getting meaner" so much as "LEGO staying true to the characters they're borrowing". And I assume if parents buy their kids a Star Wars LEGO set, they're okay with him being into Star Wars... and LEGO is probably the least violent incarnation of the franchise.