A federal judge blocked JetBlue Airways’ $3.8 billion bid to acquire Spirit Airlines, which the Justice Department successfully argued would amount to higher prices and fewer options for passengers. Tuesday’s ruling determined the proposal from the nation’s sixth-largest airline to buy the seventh-largest carrier — which would create the country’s fifth-largest airline — threatened to end healthy competition between discounted carriers. “Defendant Airlines currently compete head-to-head throughout the country, and that competition, particularly Spirit’s downward pressure on prices, benefits al…