Why 100% split? Why not a fractional share with a dollar cap, like social security? That could rednce the effect of freeloading, while still providing security in case the richest of you feels less generous in the future.
This reduces the chance that any sibling will have a lifestyle that is relatively more affluent than the others. And when we get a freeloader, it encourages the other siblings to not give up on his life. It may be easier to give up if you can tell yourself "well he is getting what he deserves".
This assumes a great deal of good faith, obviously. It can easily go bad and turn into resentment if (a) we get a freeloader and (b) he remains a freeloader all his life. But even in that worst case scenario, the hope(from our cultural upbringing) is that there will be less resentment(for the financial unfairness) and more sadness/empathy for the sibling who went the wrong way all his life.
My father's brothers have been on this model for couple decades and it has mostly worked out. They've had multiple freeloaders at one point turn into super productive contributors a decade later(and after lots of hardwork by the non-freeloading siblings towards the freeloaders).
This model is most easy when you are still young and life is simple(as it is for us now). It becomes very challenging after we all have wives, children and grandchildren and different local interests and politics. It usually leads to (somewhat bitter) splitville where assets are divided. This is one area my siblings and me are most weary of and want to do a better job of than our prior generations.