The fact that we've unintentionally wiped out so many species lends credence to the idea that, on average, very few individual specie are all that important. Of course, just leave it to us to find the exception someday...
And introduced destructive species like kudzu and the grey squirrel. These have results which are certainly bad, but far far away from causing any kind of catastrophic ecological collapse.
The demise of the Red Squirrel (in the UK) maybe more due the the loss of habitat than than because of the Grey Squirrel. The Grey Squirrel may just be a convenient scapegoat.