1.) The insurance is more expensive.
It doesn't have to do anything with your transmission. It really depends on your age and your driving record. I had 4 RDs when I was 16-20. When my parents were paying my insurance back then, it would be $400-$600/month depending on what car I drove. My record has been squeaky clean since my last RD 5 years ago (until recently
). The 335i and M3 are both <$85/month each for insurance, and other car I drive is <$105/month. If you don't have an absurd driving record, you should be alright with your insurance quote, especially if you're splitting it with your parents. Absolutely make sure you shop around because the quotes can have an incredibly wide range. Some companies were quoting me $200-$300 on the 335i and M3 when Geico quoted me $81 and $84.
2.) It's a distraction.
Since they're stating it's a distraction, just tell them you'd be more focused on the driving aspect since you'll be shifting. You can also tell them you won't be able to eat food, text, or do anything else while driving so it'll be safer. (Although that's a lie)
3.) There is a smaller market for them therefore its harder to sell.
There's undoubtedly a smaller market for them when you're trying to sell it, but within that small market, there are (die-hard) enthusiasts who've been searching a good amount of time for a 6MT. If you look in the Marketplace/cars section of the forums, you'll see a lot of "WTB: 6MT" threads. If you're trying to get rid of it quick, I'm sure the 6MT wouldn't help you. If you and/or your parents have all the time in the world, then the 6MT wouldn't be that much harder to sell.