I am mostly a beer brewer, but recently I have begun experimenting with fruit wines. In contrast to beer, the wine recipes I am using all say to do the primary fermentation with only a towel or other loose covering over the vessel, and only add an airlock when it is time for the secondary, etc. fermentations. My instincts tell me that this is a good way to get an infection, but all of the recipes I have read suggest the technique. Would it really make a difference if I used an airlock anyway?
wine's primary fermentation can be airlocked if you like (I've done it with no problems). But if you're fermenting on the fruit then you'll want to stir the fruit back into the fermenting must a few times a day (this is called punching the cap) to keep any particular bit of fruit skin from growing mold (the active yeast fermentation will outcompete any challenging microbes).
Stirring also adds oxygen which the yeast uses to reproduce/increase their population making the primary fermentation a more hostile place for infection microbes.