More residual sugar, more likely to get infected?

I mentioned this in another post I made but didn't really get any responses on that point. I'm wondering if anyone has had experience to back this up, particularly in brews with lactose or maltodextrin in them. My only infected batch was a stout with 1/2 lb of lactose in it, and that got me thinking about why that could have been. Maybe just bad luck, but maybe it was the leftover sugar. Brewer's yeast does not eat these sugars, but that's not true of some types of wild yeast or bacteria. To me this would indicate that wild yeast or bacteria are more likely to start growing in a beer where these "leftover" sugars are present. Has anyone else had experience with this or looked into the science of this?

spit does not ferment the sugar. the enzymes in the spit perform the mashing (unfermentable sugars are broken down into fermentable sugars by enzymes).

dextrose does not cause infections. unsanitized/improperly sanitized equipment causes infections. the wort is sterile after you boil it for 10 or more minutes. after you cool it, something has to infect it in order for it to turn sour.

Something has to get into it to infect it of course, but there is never a batch of homebrew brewed that doesn't get something in it. Any time your beer or a post-sanitization utensil is exposed to the air for even a couple seconds, it is exposed to all the airborne contaminants contained in air, i.e. wild yeast. The question of whether or not the beer develops a full blown infection has to do with whether any nasties can really get a hold on your beer. My thinking is that the presence of all this sugar makes it easier for them to do so.