In the world of HGT ( the horizontal gifting of genetic material between different strains or species) there is a big but frequently un-remarked difference between symbiogenesis and natural transformation versus conjugation and transduction.
In the first two instances, the receiving being voluntarily took up the foreign DNA itself, either by swallowing a living being whole or by gulping down some of the DNA from a dead or secreting foreign being.
In the latter two cases, an invader forces some foreign DNA upon the receiving being, a situation frequently called 'infectious heredity'.
Now HGT, either type, is always very risky for the individual receiving being - though I argue that it is strongly beneficial for that species' overall membership (all trillion x trillion of them) as a whole.
With numbers like that, bluntly put, the group can afford to see a billion individuals OD from "Bad HGT" on the off chance that just one individual lives on with an extremely valuable new gene function.
That individual doesn't need to take over as the new alpha bacteria either, it is just enough that this freak, along with millions of other freaks, is allowed to live on, waiting for that day when they can turn on their new gene function and win the day when a global crisis erupts for the group.
Microbes don't seem to have evolved to the level of us civilized beings, where we created Aktion T4 killer groups to set about reducing our human gene pools of all its freaks.
The microbes let their freaks and defectives (their avirulent R types) live on among them, because one day that genetic defect might just turn out to be a genetic benefit in changed circumstances.
The Nazis ran out of time before they could gas everyone with CF, sickle cell and excessive iron disease etc.
Just as well, because the milder versions of these defects are now considered to have saved the human race from otherwise all dying in sudden pandemics.
Evolution by Inclusion tolerates freaks and defectives.
It seems to have worked for the microbes for four billion years.
Maybe we humans should give try it just this once, to ensure we at least get through the next four tee years ....