Dude, scale and circumstances matter, the least painful possible example of something may genuinely be ok, but the most painful possible example isn't necessarilly ok due to the least painful possible example's standards.
Let us take the exact same example you gave us to prove how much scale matters: few would say that giving 5 dollars to a starving beggar to do some small busywork for you is cruel, or evil. Yet few would argue that giving him 1000$ for his kidney isn't cruel or evil. That is because, imho, ideals aren't always things that interact on an absolute manner, you can't say that if the smallest possible example is ok so is the biggest, or vice versa, that if the biggest possible example is unfair so is the smallest. There is a reason law has theft and grand theft as different offences, there is a reason people are sympathetic to someone stealing to feed his family but not someone who steals to get rich even if both are in similar circumstances otherwise, there is a reason disciplining your children too litle is as bad as disciplining them too much.
In our world, lines are not always clear. And yet, the kidney example I gave is something that would affect a person less than a marriage, so I would argue that coercing people into an arranged marriage is worse than buying kidneys.
Now, I do think that just like the law recognizes certain excuses in order to let people get off with lesser sentences, so should morality recognize excuses for cultural factors. People are, imho, less culpable for certain (not all) wrongdoings depending on their culture. But that doesn't make the wrongdoing less wrong, just the person less culpable (or maybe in some cases even not culpable). Ling Qi, however, does not get that excuse. She is one of the people that SHOULD know better, because just like in any culture there are people who think "hey, this is wrong", so should a protagonist who was specifically burned by that kind of thing, and who had a friend that was also burned by that kind of thing and a mother that was burned by that kind of thing.