You don't know that. Even then, as I've noted before, people have made fun of Leonardo DiCaprio's character from
The Revenant being attacked by a bear without it meaning that the attack was poor storytelling. I think sometimes it's visceral and intense moments that cause people to use humor and simplification to deal with their feelings and reactions. Seeing someone as macho and iconic as Batman soften at the sound of his mother's name and the sight of a couple in love seems to be one of those moments.
It's fascinating to me because the film itself explores the contrast between brutality and vulnerability. For example, Senator June Finch repeatedly emphasizes that conversation is the key to democracy, and she denies Luthor's attempts to acquire a deadly weapon as a means of deterrence. Furthermore, while Batman froths with paranoia and rage, and Jonathan's memory reminds Clark of haunting nightmares, both Bruce (by Alfred) and Clark (by Jonathan) are reminded to look to relationships for ballast: Alfred encourages Bruce to find a mate and start a family while Jonathan encourages Clark to embrace the light and hope the woman he loves offers him. Even Doomsday, who has always been a very symbolically rich villain, is representative of that famous quote from Dr. Martin Luther King Jr.:
The ultimate weakness of violence is that it is a descending spiral,
begetting the very thing it seeks to destroy.
Instead of diminishing evil, it multiplies it.
Through violence you may murder the liar,
but you cannot murder the lie, nor establish the truth.
Through violence you may murder the hater,
but you do not murder hate.
In fact, violence merely increases hate.
So it goes.
Returning violence for violence multiplies violence,
adding deeper darkness to a night already devoid of stars.
Darkness cannot drive out darkness:
only light can do that.
Hate cannot drive out hate: only love can do that.
In short, I don't think the reactions to the Martha scene should be taken so literally as reflecting the quality of the scene itself.