Help translating the phrase, "was seen as."
I think "be seen as" can be translated as "被视为"/"被看作"/"被认为"/"在...眼里看来是". 

As you mentioned, there should a noun following "视为", so we need to add it, however, in some informal situation, like in speaking Chinese, without this noun it's still ok. 

In some case of English-Chinese translation, it is very common to change passive voice into active voice to indicate the subject by context, which is more close to Chinese language. In the translation below I use "People"(人们) as the subject, which can be changed in the certain context.

Here is my translation of "Revolution was seen as desperate and dangerous."

（过去）变革在人们眼里看来是铤而走险的举动。

（过去）搞革命被人们视作是铤而走险的举动。

（过去）人们认为变革是铤而走险的举动。

（过去）人们视搞革命为铤而走险的举动。