What's presented to us doesn't really indicate whether he gave his consent to the experimentation of unborn fetuses or not, and absent evidence showing him okaying the project I'm going to assume he wasn't involved in it.
also I never said Gast wasn't responsible at all either, I just said he's not equally responsible to Hojo and Lucrecia.
And again, V, you're implying that incompetence and compunction are mutually exclusive. Yes, he had a conscience, but Gast was wrong in his assessment of Jenova, and without making such a mistake Sephiroth would not exist.
Do you seriously think that? Shinra pretty much proved through its actions that it didn't give a tin shit about the risks of injecting people with Jenova cells, especially since it continued doing so even after the dangers became obvious. Sephiroth himself might not exist without Gast's involvement, but someone like him would've been created whether Gast was involved or not, due to the fact that Shinra vastly overestimated the amount of control it had over its experiments. This happens so consistently throughout the course of the plot that it can almost be taken as a given that Shinra will fuck up by thinking it has more control over its science than it does. The only way to prevent an event like Sephiroth's from occurring creation would have been to destroy Jenova so that the experiments couldn't take place, and the game doesn't entirely make it clear whether that would even have been possible. Though I suppose as head of the science project Gast would've had more ability to do that than anyone else. As I said, Gast can be faulted for not destroying Jenova when he came to discover her true nature, but apart from that the worst I think he's guilty of is naïveté.
edit: though I think it's also worth pointing out in hindsight that even after you take into account the guilt he felt over his experiments, he
still might not have fully understood just how dangerous Jenova was until he interviewed Ifalna, by which point it was too late for him to go back and destroy Jenova.