Talking of assumptions: why do you assume that there is any life in space at all, and if so, why there must also be "intelligent" life, and that it is possible for civilization to be significantly more advanced than ours. Just think about it, these are all just assumptions. No life has ever been detected in space despite centuries of astronomical observation. Even if life does exist within detection distance, there is no evolutionary necessity for "intelligence" to ever appear. There are literally millions of species on Earth and only one that I dare say you would consider "intelligent". That gives you an idea of the odds against "intelligence". And finally we have no reason to assume that it is possible for science or technology to advance beyond what we have today, simply because we have no examples of such science or technology available to study.
Your oft-quoted quip about scientists in bygone days is not relevant. remember that back then they did not even have electricity so their understanding of the universe was very restricted. Today we have observed and learned to understand everything from quarks to quasars, and are in a vastly better position to see what is possible and what is not. And in particular there is nothing in there to indicate that interplanetary travel is even remotely possible.
Over a century ago there was a period of tremendous advance in the physical sciences: the theory of electromagnetism was developed, relativity was formulated, and quantum mechanics was built into a massive theory from almost nothing. What has there been since to match these huge advances? Right, nothing. A whole century has made little headway compared to the huge advances of a century ago. So why is physical science suddenly going to take off now after a century of torpidity?
Carl Sagan changed his mind as the data came in, like any good scientists would. Back in the sixties and early seventies he was convinced about finding life so easily that it would surely be found on Mars. But as time went on, deep searches were done, and nothing found, he realised what the data was saying. To paraphrase him: "There is nothing in the data to indicate that anyone is going to arrive from the sky to save us from ourselves". He realised that the idea of detecting life in space was a dream of a bygone era, and it had long been obvious that ufos were nothing more than "aberrations of the mind and public nuisance".
I realise you are probably very young. Try to keep an open mind. All that pressure you get from the media to believe in space boogiemen, ufos and the myth of eternal progress, is designed to profit from you and other users through click baiting and merchandising. Try to learn to question opinion, especially opinion of the public, insistent, and frequent variety. Always require data, evidence and preferably proof. As to life in space and the myth of eternal progress, there is no such data. As yourself then, why the strong opinions opposing the data?