Is it reasonable to ask someone you care about to stop drinking?

...if you feel like it is harmful to them and affecting their relationships with other people, and covering deeper problems?

I don't drink, but it seems that 4-8 drinks a day, everyday, is kind of extreme.

Do normally functioning people drink within that range on a daily basis and live "normally"?

I have mentioned before that their drinking behavior concerns me, but it is brushed off and justified as not being a big deal. If it's someone I care about, is it worth intervening, or do I stay out of it?