Realistically, you should be afraid of jumping and the D2 punish is probably the best case scenario. In most 2D fighters a jump is a calculated risk, with the downside being that you get anti-aired and your opponent converting that AA into big damage to capitalize on your mistake. Learn each character's anti-air capabilities (AAs in MKX are not created equal) and feel out your opponent before taking the risk of a jump in. Is his reaction time good? Is he making good reads and punishing appropriately? Is he playing footsies that show knowledge of your character's jump arc and jump in attacks? That being said, an empty jump is safe if allowed to land IIRC, a jump in punch connecting is a guaranteed combo, and a blocked one is almost guaranteed block pressure; weigh that against the negatives and you'll get a feel for what situations are appropriate for jumping.
