The motives behind the letter are to condemn the proposed policy.
I assumed you were smart enough to figure that out. 
Mr. Connolly came here unskilled and poor and raised a family and served in the military and he's upset others in his situation may not have the same chance. 
Lastly, it is still okay in this country to criticize the president and proposed legislation. 
It's too bad if that displeases you.