Every parent does things differently, and that doesn't necessarily make any of it wrong. Every kid is different and it's up to parents to know their children and determine what they can handle. Sometimes when you push a kid to do something they're scared of, they turn out to love it, and other times, they hate it. Just the same, not ever pushing your kids to do things they're scared of can make them feel more in control of and respected for their own decisions, but for some kids, it can lead to an increased fear of the unknown that builds up over time or resentment down the road towards their parents for not exposing them to more things when they were young. Honestly, every outcome is a possibility and while pushing one kid to do things may be beneficial, pushing another could be terrible. Strangers have no idea what another kid is like, so it is unfair to judge the decisions of another parent without knowing the kid.
In regards to making a kid ride something being nothing like making a kid eat vegetables, I completely disagree. If you have a kid that eats peas but is afraid of broccoli, it could be argued that the kid doesn't need to eat that broccoli since they eat other vegetables. It won't hurt their diet if they don't eat it, but most parents are still going to force their kids to try that broccoli for the first time so they know if they like it or not. Food can be every bit as traumatic as a roller coaster/ ride. My daughter, who loves broccoli but hadn't ate it for a while, FREAKED OUT in a restaurant a month or two ago, bawling, trying to run away, screaming, "NO! NO! I'm going to puke!" All over us trying to get her to eat broccoli, after knowing she loved it in the past. I picked her up and carried her while she was still kicking and screaming out of the restaurant, while everyone in there looked like at me like I was torturing her. After talking to her, I got her to come in and eat the broccoli with tears still streaming down her face. After the first bite, she smiled really big and said, "Wow, this is actually pretty good." I'm sure people thought we were horrible for making her eat it when she was so OBVIOUSLY afraid of it, but I knew my daughter best.
To contrast, when I was a kid, my mom made shrimp scampi and I refused to eat it. She forced me to and I got sick. She said I made myself sick and over the years continued to force me to eat it, even though every time I'd spend the rest of the night in the bathroom puking and with severe stomach cramps. I found out years later that I have a shellfish allergy. I still feel nauseous whenever I smell it, though I'm sure it's because of the memories of being forced to eat it rather than the smell itself triggering the nausea. My mom forced me to eat something I was allergic to, but she didn't know I was allergic and thought I was being dramatic, which is understandable considering I also swore I hated eggs, but loved omelets when she told me they didn't have eggs.

Her forcing me to eat shrimp did not make her a bad parent.
Forcing a child to ride something they are afraid of also does not necessarily make someone a bad parent or constitute child abuse. Kids have crazy reactions to sometimes the smallest of things and many times just fear the unknown. A stranger has no idea why a kid is refusing to ride. My cousin refused to ride Splash because she was convinced it went upside down and wouldn't accept that it didn't. Her parents forced her to ride it, even though she was bawling and other people looked horrified, because her parents knew her fears were completely unfounded since Splash doesn't go upside down.
Don't be so quick to judge other people's decisions when you really don't know them or the child.