I dont think it's stupid move from Uma at all.
He always been righteous and stood with his principles as always as before.
He had those strong emotions towards his family and responsibility as before. In Saras case also he cried out before Bholenath for the fate of his sister
but because of Maasisa's blind teachings he thought he dont have choice to make his sister happy at that time.
But over time he started giving importance to his own emotions that he tied with strong blind belief in dharm.
We can see how he chose Kanak over his promise to Massisa and his dharam.
It doesn't make him any less righteous at that time to break his word to Massisa but showed us a new Uma Shankar who choose his emotions over his blind belief.
Even now Uma is same Uma but he able to understand Suman more deeply.
Suman completely broken and crying at that time. She is so afraid to face anything.
Uma knows Suman didn't do it purposefully.
More over he don't have luxury of time. We clearly saw how Uma smartly stopped Meera and Akshay's plan just in three days.
He would have been able to do same at that time too but in minutes he cant do much more than agree to save his sister.
I am sure Kanak would have done exactly same in place of Uma.
How can any one will have send their sisters to Jail even it's for kids.
Suman would hv been stamped as criminal by whole cruel society.
We are still questioning Uma and saying Uma wrong for his moves but what would be Suman position.
Suman would not been alive if Uma took such step at that time.
I really support Uma's care and emotions in hiding Suman's truth before society even it is not lawful.
In Uma's place I know I would have done exactly samething and I am sure people may able to write 100 things in paper but action wise we know in india we dont go and report like that and face such consequences that will be dreadful for any adult elt alone a child like Suman.
It's difficult time for us too where our leads are going through lot of painful emotions and hope we support our leads fully with our hearts and understanding.
Finally the reason why I love our KanUm is because they r not perfect but they always give first preference to their family in that way they both think same.
The choice would have been same whether it's Uma or Kanak in that situation .