Before the blind to the Gentile

This is an impossible answer.
First of all, the sages lived under Roman (or Parthian) rule and came into close contact with the Gentiles around them, and probably knew that they did not believe and did not accept.
And second, there are commandments of the sons of Noah that are controversial among the sages, so if the sages who labored to study them did not necessarily know whether it was forbidden to a son of Noah or not, why would some Pliny know?
Of course, the sages simply did not accept the idea of rape in opinions (not that they did not recognize the reality that was before them, and which is not fundamentally different from today's reality in this respect). They simply did not interpret reality as rape. But even if a person labored and studied and erred in his opinion, there is a certain guilty factor in them in their opinion and he is not completely raped, even if there is apparently no motivation for a person to learn.
After all, there is no real difference between a philosopher who lived in ancient Greece and an atheist today in terms of the level of guilt (if anything, then the opposite is true, a modern-day atheist has a higher chance of changing his beliefs, because knowledge is more available to him and encounters with those who hold views different from his are more common).

I completely disagree with you. It is clear that in their opinion that person is not a coercive. And if you ask yourself, you will understand that the truth is that he is certainly a coercive. Therefore, it is only reasonable to conclude that the Sages truly thought that he was acting out of instinct and did not recognize the modern phenomenon of the secular (non-believer). They attributed this to lack of knowledge or instinct. So woe to the Milfin, and therefore he is negligent and not a coercive. In the mitzvot that are disputed among the sages, the sons of Noah can clarify what the ruling was and observe it. And regarding them, it can also be said that they would indeed see the son of Noah who believed differently as a coercive. The discussion is about the son of Noah who does not observe not because he believed differently.
Ultimately, in my opinion, it is impossible to say otherwise.

I completely agree that in their opinion that person is not a rapist (there is no punishment for rape). But according to their system, a modern-day atheist is also not a rapist.
They were aware that Gentiles have a coherent worldview and theoretical beliefs and philosophies (and this is no different from a modern-day atheist in this respect).
But this was not enough for them to define him as a rapist, because they expected even someone who is very far away and mistaken in his own eyes, (and who apparently has no reason to act in the way of the Torah) to find the path to truth, and whoever does not find this path is to some extent his own fault and negligence in their opinion.
You disagree with them, but you cannot bend their words to your opinion.
After all, it is clear as day that an Athenian philosopher or a member of a Teutonic tribe in the Black Forest in the first century AD is closer to rape than a modern-day atheist Israeli.

If they expected then I have no argument with them. It's just that today it's impossible to expect. It's what I said. And certainly a Gentile in their world is closer to an Israeli atheist in our day.

There is clearly a debate.
Whoever expected then, has no reason not to expect today. And how could a Gentile be closer? What reason would any Greek in Athens have to think that one should believe in the Torah that was given to a small, remote people hundreds of days' sail away, and to travel there to check whether or not it is permissible for him to eat the sinew of a sheep? And even if he had traveled there, why would he be expected to believe in the Torah and adopt its commandments? He was not educated in it, and he has a completely different perception of the world.

What is called a philosopher was a negligible and irrelevant minority. The majority of all the Gentiles that the sages met certainly believed in idols and in the God of Israel, and therefore, in their opinion, there is no rape here.

It is true that the philosophical minority developed over the generations until it became the secular majority today, but do not throw the present into the past.

If anything, another question, the Mishnah says that whoever loses a coin and someone else finds it, God Almighty determines a reward for him, and apparently according to the Rabbi's method, there is no reason for this, since there is no mitzvah here?
I thought this was in the sense of a right being transferred by a rightful owner (in the reality of providence) and quite difficult.

Most Gentiles believed in idols, that's true. But there is no connection between belief in idols and belief in God and his teachings (and atheists also believe in Spinoza's God; it's just sharing the name in both cases).
And rape is the same rape (and perhaps greater), also a mistake in art and opinion, without any clear motivation to investigate further and pursue the hidden truth. It also doesn't seem that the sages treated Epicurus and his fellow philosophers as rapists.

The above adage is not at all disturbing. These are adages, which probably don't talk about a reward for a good deed.

The Sages saw before their eyes people whose religious beliefs were clear to them, and even if they were wrong, it was just a matter of information and clarification and that was it. They did not dream of people who disbelieved because they did not believe. Those who, even if everything was explained to them, would not accept. The concept of a captive baby reflects this in the best way. From their perspective, it is just a lack of information. Today, it is clear to any reasonable person that this is not a lack of information, and therefore applying the concept of a captive baby to our day is problematic.
It was possible to understand that this was just a mistake on the part of the Sages, and in fact, even then they were clear and radical disbelievers, just like today. But if we accept their factual diagnosis, the conclusion is, as I said, that the situation has changed: back then it was clear to everyone that there is a God and that one should worship Him, and what was missing was only honest research and information. Today, it is certainly not clear, and information will not necessarily change the atheist's positions.
It is clear that there were such figures even then, but it was a minority that the sages did not recognize or at least did not find it appropriate to address because of its neglect.
I think we are repeating ourselves.