This is about making decisions and using rational thought, not about if said app developer is at fault for the inclusion of the feature. The developers of Snapchat added this filter just to spread a general message about not Snapchatting while driving and kept it as feature. It literally states in the snapchat filter "Please, DO NOT snap and drive" right above your MPH. Their terms and services explicitly states

"Do not use ours services in a way that would distract you from obeying traffic or safety laws. And never put yourself or others in harm's way just to capture a snap." The filter itself contains a small warning that says "don't snap and drive."

The fact is that there always will be idiots in the world who will not think before doing something. Someone will always use something new or innovative for something bad that will result in injury or some form of damage, no matter what the product is, may it be an application, a piece of technology, a purchasable service, etc. The persecutes have released this statement that claims that "in a time where distracted driving is on the rise. why didn't Snapchat, a successful think about the repercussions of releasing the MPH filter and the fact that people will want to try and gain the most trophies and points possible, no matter the cost. There have been multiple other occurrences of death and danger caused by snapchat." There might be points gained by posting an MPH snap, but there is no such snapchat trophy for getting a certain speed, which can be cross-refrenced here. They also reference other cases against snapchat, such as the data breach and when they were sued for technically saving snaps, which they claimed disappeared after a certain amount of time. A Snapchat spokesman has even said "No Snap is more important than someone’s safety. We actively discourage our community from using the speed filter while driving, including by displaying a 'Do NOT Snap and Drive' warning message in the app itself." In the end, it comes down to people, not the app itself. Snapchat might be liable for the creation of the MPH filter and its implementation, but they are not liable for how their users use the application. I believe that Snapchat is somewhat responsible for the implications of the filter, but they aren't to blame. It most definatly is the driver's fault for even thinking about snapchatting while driving, and it the end the lawsuit should mainly focus on them rather then trying to fight the multi-million dollar company.