There's a fascinating history of mens facial hair, if people like history ... it's had vogues in classical times, and gone out of fashion. Caesar was clean shaven, (and didn't you know it) whereas later emperors were quite heavily bearded.
In fact the 20th century is probably the cleanest shaven in 2000 years. Presumably because of the necessities of wearing gas masks.
There's also been a status thing about male facial hair - if you think of the increasingly ludicrous moustache styles of the Victorian and Edwardian gentlemen - clearly a sign to all that they didn't need to work for a living.
Then the 1960s (or even 1950s) counterculture making beards a statement of rebellion.
The fact the word "barbarian" entwines the Greek "bar bar" with the latin "barba" in reference to uncivilised cultures (i.e. non-Greek or Roman) is also fascinating.