In chapter 46 the Roshei Avos and Nessim present their complaints to Moshe. Their complaint is that if the daughters of Tzlafchad are given the inheritance of their father, they potentially could marry out of the tribe and that land which was part of the tribal division will then suddenly belong to a different tribe. Eventually there would be chaos with different tribes possessing parcels of land in various tribal areas. Specifically they were worried about their tribe losing parcels of land.
Moshe responds with an answer from Hashem that such women who inherit because there were no sons to inherit should only marry within their own tribe. This would ensure that the lands would stay in the original tribal division.
In verse 10 the Torah tells us that as Hashem commanded Moshe, so acted the daughters of Tzlafchad. It then proceeds to tell us that they married their uncles, thereby keeping their lands in the same tribal division.
Why did the daughters of Tzlafchad have to go through the whole process of arguing for the inheritance if at the end of the day they were going to marry their uncles, who would have been next in line anyway to inherit the land had the daughters not stepped forward? What did the women gain that gave them reason to argue as they did?
The Seforno and Ohr Hachayim seem to be answering this question. They each suggest that the command of Hashem that women who inherit should only marry within the tribe did not apply to the daughters of Tzlafchad. They had already been given permission to marry whomever they so desired. The fact that they chose to only marry within the tribe shows they were doing so to set an example, even though they did not need to.
I would like to suggest a different answer. It could be that they did not need to marry in their own tribe and this was a selfless act to set an example. However, they could have married some other nice young men from their tribe. They did not need to marry their uncles. It seems to me that the fact that they married their uncles indicates that they originally intended to regardless of the fact that they did not have to. In fact it was very common then to marry relatives, uncles, cousins, nieces, etc.. So the chances are that this was the original intention anyway. So my question still stands, why did they have to go through the whole issue if they were planning anyway to keep it in the family?
I would like to suggest this answer. They were arguing the point purely for arguments sake. They felt it necessary to be the precedent. Sure, it did not really make a difference in their case, but they saw an injustice happening and that would affect many other women in the future, even if it did not really affect them. They were willing to stand up and put themselves in the line of fire, so to speak, to set the precedent for future scenarios similar to theirs.