"n-다는" here is providing extra details for "의견" or the "opinion" that is being talked about.
For example, "그가 살아있다는소문이 돌았다" can be translated as "there was a rumorof him being alive" or "a rumorthat he is alive circulated". Here, "-다는" directly describes "소문" or the "rumor" being spread around. It is used to specify what kind of rumor is going around: the "rumorthat he is alive."
So, your translation of "-다는" is in fact on spot. Just like how you've translated the sentence, "that" or "which" as a relative pronoun can be an English equivalent for "-다는", as can be seen in the aforementioned rumor example: "rumor that he is alive" (or "the opinion that it was an example, a role model, a living proof, etc.).
With that being said, if you are going for a literal, word-to-word translation, "the opinion that it was a (shining) example/a role model/a living proof/exemplary instance was widespread/almost unanimous" ("the opinions were many," just sounds awkward and unnatural.). If such is not the case, in English, it woud be more natural to say, "most believed that it was a (shining) example/a role model/a living proof", "it was widely considered that ~ was an exemplary instance", "the general opinion was that ~ was set as an example", and etc.
Just a side note, some additional details or contexts could help the forum interpret the sentence more accurately. For example, the subject of the sentence is missing so it is unsure what serves as "an example" (or "본보기" in Korean) and whether the writer is connoting something positive or negative. Bear in mind that depending on different contexts and situations (and just as in English), "본보기" can convey a positive connotation, such as a role model, an (shining) example, a living proof, etc.or imply a negative "example", such as "punishment to set an example". Either way, the word itself is translated as "an example, proof, model". Hope this help!