I think they acted precipitously in destroying the Cell from their Universe, 

as they could have raised him from birth and have Bulma work out any technology related programming that would be detrimental so that the Cell from their Universe would be good and on their side as an ally against the bad Cell from the future and there could be a good vs bad Cell fight, 

The good Cell would probably figure out how to boost their energy within their first form past that which The bad Cell would be able to do so within their ‘perfect’ form, 

Thus proving that they wouldn’t need their other forms to realize their potential maximum power which would lead them to decide that not absorbing 17 and 18 would make sense, 

Good Cell beats bad Cell, 

For some reason I’m becoming intensely sad within, 

I live, 

Literally,