It's the evangelical Christian vs. the guy who beats his girlfriends.
The linked Kevin Iole article comments on how Mayweather's half-dozen charges (and one jail sentence) for domestic violence have been largely ignored in the build-up to the fight. It's a good article, and correct, but if you really want to see the lack of seriousness with which our society as a whole treats domestic violence, look at the fact this fight hasn't even been grazed by the good vs. evil brush.
As much as Mayweather has done well promoting himself as someone who can easily be disliked- customers who pay to see you lose are still paying customers- his team spins that off of his personality and relatively mundane behaviors, such as how he spends his money. And Pacquiao's team might have good reason not to attack him on those grounds either: it's hard to imagine a large potential audience that doesn't plan to tune in now, but would specifically to watch a known domestic abuser get beaten up. Compared to how many people could decide to boycott the fight in order to avoid putting more money in Mayweather's pockets, it would probably end up costing Pacquiao money to hit this angle particularly hard.
And who knows what Mayweather's team could dig up about Pacquiao's pre-conversion history...
What about the rest of the media, though? The idea of truly neutral journalism is largely a fallacy; neutral wording doesn't change the choice of what stories are covered. It's not surprising to see Mayweather's record of abuse go with minimal remarks most of the time, but if you're covering a fight like this in a country like the U.S., with its substantial overall religiosity and substantial evangelical population, how do you not spin the story this way to pull in the entire Bible Belt as readers?
Is it because Pacquiao's not American? That would affect the perception of some, but it's not as though American Christians have stopped partaking in or supporting overseas missionary work. Plenty of people love his come-to-Jesus story, and plenty more would if they knew about it.
Is it because Mayweather is American? More specifically, a rich, successful American? This is trickier to contemplate. The U.S. still has tons of issues with what one might call "subcutaneous racism"- the kind that sits just under the skin, unnoticed but ever-present, that can make a person genuinely believe they treat people of different ethnicities equally in one breath, and in the next label a young black man they've never met and know nothing about a thug based on a single report of a single newsworthy incident.
Given that Mayweather has done enough to earn that sort of negative perception, it seems like painting him as the devil to Pacquiao's avenging angel should be easy. It may not seem that way if you look at, for example, any comment section on any web article about Mayweather's domestic violence history, but those articles are always specifically about Mayweather's abuses; in something more comparative between the two fighters, there would probably be a lot of comments such as, "But Pacquiao's still obviously the better person," if for no other reason than he's found religion.
Is it because the good vs. evil angle is, as always, oversimplified and not entirely true? Consider what the effect of this would be: any comparison of the two, where Pacquiao is the bastion of morality and Mayweather the terrible fiend, would set off a firestorm between people bashing Pacquiao's past or lauding Mayweather's positive deeds, and those who take the current situation and cling to the absolutism good vs. evil provides. What media outlet would turn down that sort of attention on their work? There are a few, probably, but most live and die off hits, and this type of article would be a hit magnet.
So why isn't anyone going after this story?
Sadly, the best guess here is that hardly anyone considers it a story at all. Relatively few people are open apologists for abusers like that fucking prick Stephen A. Smith, but boxing media is almost entirely male, and plenty of men- especially the older ones who disproportionately populate that segment of the media- still question the veracity of domestic violence accusations, how much it matters even in an instance where someone famous went to jail (which is rare like birds' teeth), or- at best- how to approach this topic. Iole has an enormous platform at Yahoo, but he is very much an outlier in the importance he places on the topic. And the nature of the boxing economy makes it so there is no way to punish Mayweather the way the UFC just did to Jon Jones- title belts are ubiquitous to the point of meaninglessness, and the only thing Mayweather would ever be suspended for is a failed drug test.
To be literary about the matter, it's a whole bunch of bullshit.
I'd like to see Pacquiao dump Mayweather on his face. I want to see that enough to feel like any prediction would be skewed by the feeling. I'll stick with the low-hanging fruit: a fight ended by stoppage will be won by Pacquiao, a fight that goes the distance will be won by Mayweather.
And then they'll have all the issues involved with deciding how to spend nine figures worth of money.