Since there have been a number of people claiming "valid" arguments are not being put forth for the male Viera I have included a couple below, which have been formed from SE's own written lore.
Below is a quote of Viera lore taken directly from the Shadowbringers mini-site:
This lore provides support for male Viera on two counts:Of tall stature and slender frame, the Viera's physical appearance is strikingly similar to that of the Hyur and Elezen, save for their distinctive long ears. Adhering to a strict code known as the Green Word, they are prohibited from contact with the outside world under threat of exile. Their society is purely matriarchal, and males of age are seldom, if ever, found within the bounds of any village. They instead serve as protectors of the wood from the shadows, that no evil may ever encroach on their sacred lands.
Count 1 - The lore states that all Viera live life in accordance to the Green Word. Any Viera who leaves their homeland has broken the Green Word and is therefore sent into exile.....therefore from this section of the lore NO Viera should be playable including females...so for those who are adamant SE stays true to lore, then the Viera should never have really been a playable race to begin with...yet these same people very much support female Viera. This shows that there is a double standard with those who oppose male Viera based on the grounds of lore...
Count 2 - The more vital part of the Viera lore is that it states only the males live OUTSIDE Viera settlements and do so to protect their homeland from outside threats....such as Primals, Ascians, Garleans, and whatever else...Exactly like the WoL in that respect. So the official Viera lore actually supports males being playable more so than females because it's clear the males are the ones who will be the most likely to encounter said threats and outside influence.