Once again, this was covered long before I got here, but it's a subject I've done a lot of research on. I've heard so much negativity about beards from elders, even ones who claim they would like to have one if they were allowed. The fact is, only the Society has ever found fault with beards and every time God has expressed his opinion of them, it's been positive.
YOU must not cut YOUR sidelocks short around, and you must not destroy the extremity of your beard - Lev 19:27 (reiterated @21:5)
Shaving off a beard was a symbol of sorrow or destruction.
Now as soon as I heard of this thing I ripped apart my garment and my sleeveless coat, and I began to pull out some of the hair of my head and of my beard, and I kept sitting stunned. - Ezra 9:3
In that day, by means of a hired razor in the region of the River, even by means of the king of As·syr′i·a, Jehovah will shave the head and the hair of the feet, and it will sweep away even the beard itself. - Isa 7:20
He has gone up to The House and to Di′bon, to the high places, to a weeping. Over Ne′bo and over Med′e·ba Mo′ab itself howls. On all heads in it there is baldness; every beard is clipped. - Isa 15:2
For upon every head there is baldness, and every beard is clipped. Upon all hands there are cuts, and upon the hips there is sackcloth! - Jer 48:37
And as for you, O son of man, take for yourself a sharp sword. As a barbers’ razor you will take it for yourself, and you must make it pass along upon your head and upon your beard, and you must take for yourself weighing scales and divide [the hair] in portions. A third you will burn in the very fire in the midst of the city as soon as the days of the siege have come to the full. And you must take another third. You will strike [it] with the sword all around her, and the [last] third you will scatter to the wind, and I shall draw out a sword itself after them. - Eze 5:1-2
Even long hair on men, every time God gives his opinion, he seems to be for it.
All the days of the vow of his Naziriteship no razor should pass over his head; until the days that he should be separated to Jehovah come to the full, he should prove holy by letting the locks of the hair of his head grow. - Num 6:5
Now compared with Ab′sa·lom there proved to be no man so beautiful in all Israel as to be praised so much. From the sole of his foot to the crown of his head there proved to be no defect in him. And when he shaved his head—and it occurred at the end of every year that he would shave it; because it was so heavy upon him, he shaved it—he weighed the hair of his head, two hundred shekels by the royal stone weight. - 2Sam 14:25-26
Of course, we're all familiar with Samson and his 7 braids.
Paul's reason for bashing men with long hair must have been a personal one. But he's known to say things that are his own opinion: "I say, yes, I, not the Lord" (1Cor 7:12). It was no-doubt swayed by militaristic Roman custom where the fashion was for men to be "high and tight", to use current military jargon. This kept lice and filth to a minimum while on the battle field for long periods of time. It also didn't allow for an enemy to grab and use his hair to manipulate a soldier in close combat.
Of course, we all know these man-made rules are nothing more than a power-grab by (currently) 8 old men and the elders who worship them. They're not the least bit interested in anyone submitting to God, but to the GB or even some idealized personification of the publishing company, itself. Of course, we have all seen examples of people doing bad things always wanting others to join them. Other people doing it makes it seem not so bad, or even acceptable. Of course, the elders have to perform this idolatry to retain their positions and possibly some part of them knows what they're doing is wrong, so they need to feel like "everybody else is doing it" to ease or eliminate their guilt.
Interestingly, even the Society's literature doesn't overtly ban beards, but cautions to give it thought (after they bash beards, of course). The expectation is that if we want to please God (the Society), we'd never do anything He (the Society) doesn't personally like. This mentality can't really be put into words - whether printed in literature or vocalized in the back room - since it would sound totally insane and cultish. It takes years of brainwashing and mental/emotional conditioning to "get it". Purely emotional and cultural rules are impossible to present logically and just have to be "felt". This is how JWs interpret the meaning of 'putting on a new personality'. Therefore, the cautions are perceived as orders from God (the Society), rather than a plea to train one's conscience according to the Bible and obey its warnings. The actual words on the pages are completely ignored and the intended meaning is conveyed perfectly to those who "get it". It's the secret code JWs have substituted for the "pure language" along with renaming things that already had names (Old/New Testament, John the Baptist) and redefining words that already had definitions (truth, light).
A side note, on birthdays:
The excuse for the birthday ban is the 2 birthdays mentioned in the Bible where bad things happen. By that logic, Eglon - "a very fat man" - who was an evil king of Moab must indicate that being fat should also be a DFing offense. Also, Jehovah sent Ehud - "a left-handed man" - to kill him, so left-handed people should be held in special esteem in the congregation.
