fabric today ALMOST never comes to you at a 90* angle. if you rip, you'll go on grain, but it won't necessarily be on square to the selvedge. ripping also weakens the fabric around the tear further sideways out than you would think at first glance.
as a dressmaker, i was also taught to rip. as a quilter, i don't think it's important, as long as the bias pieces, such as curves, are on bias.
today we quilt the pieces down enough to hold everything in place. and by starching, we have good control of the fabric, in fact, better control than ripping and then not using starch.
if you look at antique quilts, you'll see that grain was not as important as getting the most out of all the fabric, and they held up well.
why is this so important in today's world? if you really want to construct a quilt as they were made originally, you would have to put away your featherweights and get out your thimbles.