Tsukasa said that if he and Senku would have met 3700 years ago they would be friends. How does this make sense? Tsukasa faces Senku because he wants to turn the stone world into a modern world through science. But if he would have lived 3700 years ago he would be friend with Senku and according to his imagination scenes, he would help Senku with his science. Which is the reason he opposes Senku now.
Why did Tsukasa say that if he and Senku would have met 3700 years ago they would be friends?
3700 years ago they were normal people without any possibility of changing the grand scheme of things. But now in this stone world, they both have the opportunity and will to shape how society will develop and they ended up with conflicting views. Senku wants to restore things to how they were and Tsukasa want to create a world without materialistic values. Senku wants to revive everyone while Tsukasa only wants those he considers good people.
So what Tsukasa is saying is that he likes Senku as a person, but that because he now as ambitions to live for he will have to get rid of anyone standing in the way (i.e. Senku) even though it pains him.
