If everyone were switching to Gecko, that would be horrible for the web - it would be a monoculture. If just Opera switched to it, that would be bad - loss of

If everyone were switching to Gecko, that would be horrible for the web - it would be a monoculture. If just Opera switched to it, that would be bad - loss of one implementation is almost always bad - but it would at least maintain some non-WebKit market share in mobile. So less bad but still quite bad. So yes, I am guessing that Mozilla folks would say it would be negative (I would).