I don't think anyone is actually condoning it that its ok to stand up when the Seatbelt sign is on but the fact is when the aircraft reaches 10,000ft which is probably what was going on here since the FA was talking with you, when passengers here that DING DING and even though the FA will clearly say the sign is still illuminated and they are only authorized to use electronic devices people still get up and go to the bathroom.
However you seem like more of a hassle to the FA than the folks standing in the aisle. Let them get up. When their heads go through the ceiling because of turbulence Jetblue will not be paying any medical bills.