What if....
At some point in the future mankind is forced into taking action to cull the numbers to a more manageable level for sustaining the planet.
They believe the past is set and can't be altered so they decide to send large groups to specific points in time after sending people back 1000's and millions of years where large percentages are lost to mass extinction events, wars and pestulence they decide to send a big influx to the 1960s and 1970's only to find that this is what caused the problem in the first place and the problem grows exponentially overnight.
At some point in the future mankind is forced into taking action to cull the numbers to a more manageable level for sustaining the planet.
They believe the past is set and can't be altered so they decide to send large groups to specific points in time after sending people back 1000's and millions of years where large percentages are lost to mass extinction events, wars and pestulence they decide to send a big influx to the 1960s and 1970's only to find that this is what caused the problem in the first place and the problem grows exponentially overnight.