User blog comment:Legionwrex/Genophage good or bad./@comment-2256917-20100921213716

In a way, the krogan threat is not dissimilar to the Reaper threat (in that each group was acting on their own volition [in contradistinction to the Rachni], and willing destroyed several planets to achieve their aims). However that may be, there was no "real evidence of any impending war with the krogan" because the krogan were already waging war against the Council races. And they were approaching victory (one codex mentions that the Council races would have lost if not for the discovery of the turians and their large military). Once the turians became involved, the krogan responded by utterly ruining 3 whole planets, i.e. destroying every living thing on them, and then some. Most of this I mentioned below. -- The games give these opportunities to consider these enormously difficult problems; so we should get such relevant facts straight first.

That aside, the idea of a gene-eating virus (like most SciFi fancies) is rather horrific. But I've no idea what (in ME universe) was available as alternative measures to the galactic races, which otherwise faced mass extinction or enslavement (at a time, by the way, when human beings were still fighting with swords and horses, etc.).