I have studied a few martial arts, for a few years each. I’m not an expert, but here are my notes on this topic.
The first ones I studied were sports Judo and sports Karate. These seem to be the common form of these arts taught where I live, and are geared towards competition, rather than real fighting. In those, we were forbidden from being too brutal, and that included things like groin/eye strikes. The aim wasn’t to hospitalize the guy, it was to earn points in a refereed fight.
After those I moved onto Wing Chun. This was very different from the sports styles I had done before. There weren’t belts/costumes/padding/gloves/mats/etc. It was much more geared towards ‘real’ fighting, to the point of what you would do when the possibility of hospitalization or even death were involved. In this style, we were taught that eye strikes, groin strikes, gauging, and all the other attacks like this are fair game.
However, groin strikes where still not a big part of the teaching for a few reasons. The attacks we were taught involved mainly punching/open hand/lower arm strikes to the upper body and head. Kicking was used very little, and it was strongly discouraged to kick much higher than the shins, due to the likelihood of them grabbing your leg and taking you down that way. Another consideration was that trained fighters tend to use stances that make groin attacks less effective or more difficult. However, groin strikes were taught as part of the ‘emergency training’, which is the part of the style where the normal strict rules are relaxed, in the event of an ‘emergency’, anything that will work is considered fair game.
In the few real fights I’ve been involved in, it depended a lot on the situation whether or not I used groin attacks. A couple of fights were of the ‘honor’ variety. In those fights I didn’t use groin strikes, as it was one on one fighting, and it would be considered socially unacceptable to use those kind of techniques. It would be considered much less honorable and ungentlemanly to win in this manner.
However in fights were I was attacked for no reason or by a few people, I used those kind of attacks freely, they had dishonorably attacked me either for no real reason, or by using multiple people, so I considered there to be no social pressure to act honorably myself.