If your dogs are unrestrained in the back, they're still at risk. If you want them to actually be safe in a crash, they need to be belted in with a harness.
I agree with what you stated, but with a small caveat. If I'm going on the highway they get put in a crate in the back seat that's strapped to the cargo tiedowns. But for this post I'm talking more for in town driving, where the fastest speed I can drive is 25mph, and the worst crash I've seen around here is a few small fender bender that don't even set off airbags. And when I say safer in the back for them, I mean so that they can't be climbing around the front and jumping on the dash, obscurring my vision, or as one of them attempted before when she was a pup, to get down by the pedals. So to summarize, at any higher speeds they get kenneled in the back and the kennel is tied down, but in town at 25mph and under, that's unnecessary, and I prefer to take them with me wherever I can and let them stick their faces out the window. This isn't an attitude filled response, so please don't take it that way. This is just me explaining why I want some kind of seperator.