David Carter. What you state is entirely correct. The group do not carry the support of their peers, but that is a lonely furrow ploughed by many others in the past, who have subsequently had their theories accepted. I would not necessarily accept all they say but would certainly keep an open mind and not discount the possibilities outright.
There is a major problem trying to establish any sort of accurate chronology or frequency because oceanic impacts are hard to find and evidence of terrestrial impacts tend to be weathered out in time, also making them hard to find. Just because we have not managed to construct an accurate data base does not give us the confidence to be complacent and say it does not happen. Shoemaker levy's multiple impacts on Jupiter demonstrated very clearly that impacts do occur.
Our problem today is that we have no idea as to frequency, or intensity of possible impacts and as a result of this many do not accept we may have a problem.