Most problems can't be fixed by banging other people.
Maybe it works great for her and her boyfriend, but are sex parties really good for everybody? Um, probably not. Velde might consider herself a "sex expert" but she's definitely not a relationship expert. She doesn't understand that what works for her isn't going to work for everybody.
Here's the thing: Monogamy isn't for everyone, either, but it is for some people. Just like there are plenty of happy people in open relationships, there are plenty of happy people in closed relationships.
One isn't universally better than the other. Some people don't enjoy seeing their significant other be with other people sexually. Also, there's nothing wrong with not wanting to be with anyone other than your significant other.
The problem isn't the concept of going to a sex party with your significant other; if that's what you're both into, then by all means go — it sounds like a wonderful time. It's no different than if you and your significant other both really like movies, so you go to the movies all the time. It's simple and it just makes sense.
The problem is Velde's promotion of the idea that going to a sex party can save a marriage. Really? Yes, in very specific cases where two people are in a monogamous relationship but they both secretly crave an open relationship. Unless that's the case, then no, a sex party won't help a marriage or relationship out at all.
The whole idea of getting rid of monogamy to fix a marriage is insulting. It's insulting to both monogamous people and also to people in open relationships.
(Also, it's hard to imagine that people at the sex parties want a bunch of unhappy married people showing up. They're there to have a good time, not to help you figure out how to communicate better.)
It also assumes that every problem is sexual. If two people just aren't getting along anymore, then going out and having sex with other people won't help the problem. Bringing more people into the bedroom won't help couples who are arguing about whether or not they should start having kids. Sex isn't going to fix problems that aren't the result of sex.
More importantly, if two people are growing apart sexually, maybe they shouldn't be in a relationship anymore. Sexual attraction is an important part of being with someone.
Even people in open arrangements still break up. They don't keep returning to someone that they're not attracted to. Sometimes, it's time to move on. It's not healthy to start sleeping with other people just so you can stay with someone who doesn't turn you on anymore.
The idea that these sort of sexual interactions can help a monogamous relationship demonstrate a complete misunderstanding of both monogamy and polyamory. Pushing the idea that being more sexually adventurous is a magic cure for relationship woes is really just a way of trying to ignore the problem.
This is no different than telling someone to try being gay because their dating life isn't going well. If someone's not gay, then that's terrible advice.
It also suggests that being gay is a choice. It's the same thing with polyamory. If you're not into it, then you're not into it.
The argument here isn't polygamy versus monogamy; it's about actually facing your problems.
Spicing up your sex life might help you ignore your problems or maybe even make it easier for you to stomach them — but it won't make them go away.