This is a useless reply, and it has become pervasive. Technically anyone not a part of the solution is part of the problem. Instead maybe clarify on what you find objectionable to help everyone out, including parent.

Would you please not make this place even worse by adding gratuitous partisan slights to what is already a flamewar?

In what way is OP 'part of the problem'? If the other party wishes to also pursue a romantic relationship - what's the problem?

I can't speak for OP, but let me ask you this. Suppose your sister is in the back of a police vehicle, on her way to jail. Would you rather the cop who is driving that vehicle be told

A) It's okay to flirt with suspects/criminals if they are into you

B) It's never okay to flirt with suspects/criminals and you will lose your job if you do

?

Obviously the second.

If its your sister, if the police flirt with her, she will probably have an easier time in jail, maybe able to get preferential treatment. Good if you are the guilty criminal. So A.

If she is a suspect, then she would feel pressured to go along with the police's advances, because of the risk of retaliation for knocking back advances. So, B.

But for the victim of your sister's crime, she will want justice to be served, and will definitely go for B.