You will find just as many folks in the tear camp as you will in the don't tear camp - it's right up there with the pre-washing question. There is no RIGHT way. The way YOU choose to do it is RIGHT for YOUR reasons.
These are my reasons
I'm not a fan of tearing. There are so few times I've had to cut something *exactly* on grain that it's just not worth it to me. I'm also a heavy starcher - so having to have something *exactly* on grain hasn't been an issue. Plus, when torn the edge is wavy so I have to cut the wave off and there is not guarentee that I've cut it *exactly* on grain so again ... why bother??
I'm talking *grain* not print - which is OFTEN off grain.
When I shopped at Eleanor Burns in Paducah the gal's in there tear the fabric, they don't cut. I'm a dedicated pre-washer and I can say that my torn fabric frayed a LOT more than my cut fabric.
The last reason ... I really hate that sound