I asked Michelle Arnold directly about this. Here was her response:
Michelle Arnold:
**Please forgive me for not having time to plow through the whole thread. I will only answer what stood out for me in your question and the thread.
In the OP’s original question, both the OP and the priest were not entirely correct. The OP was incorrect to say that one of the purposes of marriage is to be “in a monogamous, loving relationship” (that would justify same-sex marriage), and the priest left out the first purpose of matrimony, more important than even procreation (which may not happen for every married couple): to form the couple (and any children they may have) in sanctity.
The priest also was unfortunately dogmatic where the Church is not by claiming it to be sinful to buy music (or any other product) from someone who supports same-sex marriage (or any other immoral act). The Church simply doesn’t make such a claim and those who say it does should be asked to provide evidence to support that claim.
CCC 1868 cannot be pressed into service here. To buy music from someone who supports an immoral act is not direct participation in someone else’s sin. I would hesitate to say that it is even remote material participation if the music in question has nothing to do with same-sex marriage. If we take this assertion to its logical conclusion, then an argument could be made that Catholics should reject the artwork of
Caravaggio**
and the plays of
Christopher Marlowe. Even if they are no longer alive to reap financial rewards, patronage and study of their works lend them legitimacy and fame. (At least under this theory, which I hope can now be seen as risible).
The confessor the OP spoke with sounds like a good, well-meaning priest. Unfortunately, when good, well-meaning priests are not well-formed in moral theology or are willing to present their own preferences as the teaching of the Church, they can do much harm to souls (especially the scrupulous, who are all too desperate to trust them). St. Teresa of Avila once said in her book Way of Perfection:
Thanks for sharing that.
I think this is an area of thought where it is very, very easy for those prone to scrupulosity to spend way too much time agonizing over the details (when they could be praying!

).
What if the money I spend on a tube of toothpaste gives the cashier at Walmart, the truck driver of the supply truck, the quality control person at the toothpaste factory, the inventory clerk at the toothpaste company’s corporate office,
and the cameraman for the the toothpaste company’s commercial just enough extra money to buy their daughters Lady Gaga’s “Born This Way” on iTunes, which leads those five girls down a secular, heathen path whereby they abandon all morals and come together to be the next
five Lady Gaga’s in 10-20 years from now sowing their peculiar form of moral perversion to millions of unsuspecting fans the world over. And all because I had to buy that toothpaste!