That includes women, children and elderly. If you count fighting age men only, 1M becomes significant. If you count men actually available for draft, you're already at 10% loss.
It always surprises me when calculation is done on a basis of formula that goes something like this. Total population - Casualties = Number
1 million casualties is an absolutely massive number, regardless of your total population. How many of your fellow citizens would you be willing to throw into the meatgrinder until you say “that not ok”?
For anybody still questioning why the civilized word must stop Russia, i'd suggest to mediate a couple seconds over the parent comment (the commenter in the parent and in his other comments presents Russian position quite correctly)
>"A casualty, as a term in military usage, is a person in military service, combatant or non-combatant, who becomes unavailable for duty due to any of several circumstances, including death, injury, illness, missing, capture or desertion."
When you restrict it to fit men of military age (lets be generous here and say 18-55 , even though there is ample evidence of Russian men 60+ signing up), 1 million is quite alot. The Russian population skews older - median age is around 40. There is also a massive gap of of people their 20s-early 30s.
Imagine all the men of your entire high school / college graduating class being either killed or seriously wounded so Putin can grab a few thousand km of territory.
Now they could allow women in combat roles, but I severely doubt it for this conflict. It would be extraordinarily unpopular and go against the narrative they have been selling their populace for decades.
1m is not a lot
Edit: as per my comment below, casualties are not deaths. It's a wider definition.