Jim Oberg wrote:

At the impact speeds of the particle collection,
it would be self-sterilizing to the nth degree.

For conventional viri and microbes, yes, assuming a head-on collision.
But assuming every particle will be at speed of 0 while the ship is at
high speed is perhaps a dangerous assumption. And assuming that only
viri and microbes known on earth are a danger to the human body is also
a dangerous assumption.

And it works both ways too. You don't want stuff on earth to contaminate
what it has collected.