Advocates of perpetual economic growth allege that the world in which we live is a better place compared to what it was a long time ago.

allege 是动词，意思是"声称、断言"，通常指在没有充分证据的情况下提出某种说法。这个词带有一定的法律意味，暗示所声称的内容尚未被证实。