Thinking that pursuit of knowledge is only activity for immortal is naively idealistic.
Elimination of of all life not like me. Or simply eliminate life that might singularity and become a threat. Even if, who's to say one aliens pursuit of knowledge latest experiment dose not require and earth sized amount of raw materials.
Our aggression reflects the zero sum physical resource context of our evolutionary past. Knowledge in contrast grows fastest through cooperation. As power including the power to defend oneself grows with knowledge, knowledge seeking entities will quickly evolve to maximize cooperation. And as many have pointed out, unlike most of our sci fi, it is very unlikely for two alien civilizations to meet where their technology levels are similar - one will be permanently vastly advantaged over the other. Aggression will be pointless - the pecking order will be obvious. As to your last point I am sure lifeless planets will do for any experiments.
Elimination of of all life not like me. Or simply eliminate life that might singularity and become a threat. Even if, who's to say one aliens pursuit of knowledge latest experiment dose not require and earth sized amount of raw materials.