Putting the pen in backwards is 100% user error. Could they have redesigned it to prevent that from occurring? Sure, with some sacrifices. There's almost always a trade-off in aesthetic for safety. These phones are super-tightly packed and one tiny increase in pen handle width could have changed the entire frame design (possibly even affected the design of the internals to the point it would have meant a major rework). However, yes, they could have done that.
What bothers me the most, though, is that people are doing something stupid, and then affecting a companies sales/bottom line by trying to turn it into some type of scandle. As if Samsung deserves to lose a ton of money because someone was "absent minded" or whatever the excuse is. Many people tried it as a result of reading the articles, which if we want to start blaming companies for the actions of individuals, also puts some responsibility in the way it's being reported by these tech sites. Do you see where this is going?
We are watching a generation evolve that can't take any personal responsibility and wants to blame someone/something else for everything they do. This is not how I was raised, and it all comes down to the issue with entitlement. I was taught that you appreciated the expensive (electronics) things you worked hard to get, and you treated them like museum art. Keeping them clean, safe, not letting your kids touch them until they were old enough to understand the value and how to respect it. Now we live in this "disposable" society where it's like "who cares if I break it, I'll just get a new one." Even if that means scamming Samsung or the insurance or the carrier. A very criminalistic mindset, but since people have no respect for large corporations anymore it's "OK" to steal/lie/cheat.
This comes down to a lot more than some "design" flaw. It's really an issue with a bunch of whiney brats that don't care about morality and would rather watch a company burn than be responsible for using the product they bought correctly.
My two cents.