Final answer:
The Lincoln family was concerned about Robert joining the military due to the dangers of the Civil War and the political ramifications of his enlistment. The enlistment of African American soldiers highlighted these dangers, as these soldiers faced discrimination and life-threatening risks beyond those of their white counterparts.
Step-by-step explanation:
The Lincoln family was worried about Robert joining the military due to the high risk of casualties during the Civil War, as well as the potential political implications his enlistment might have.
As the Civil War progressed, the issue of emancipation and the enlistment of black soldiers became pressing. President Lincoln carefully navigated the political landscape to maintain support from both the Border States and the abolitionist faction, balancing the military necessity of emancipation with the delicate Union alliance.
With the Emancipation Proclamation and the recruitment of African American soldiers, including in all-black Union Army regiments, the meaning and stakes of the war shifted.
This heightened concern for the safety of soldiers, including Lincoln's own son. African American troops faced not only the dangers of war but also systemic discrimination, lower pay, and the threat of enslavement or death if captured, as revealed in the letters from soldiers such as James Henry Gooding.
Given these conditions, as well as the personal significance for the Lincoln family, there was a legitimate cause for concern about Robert joining the military, as there was for any family with sons fighting in the war.