In my experience a airline doesn't really care how cost is divided up between a crew once the total crew cost for all seats is agreed on. In other words, a cost of $100 per hour could be agreed on to pay a captain and a first officer. The union then decides that the captain will get $80 and the F.O. $20, or whatever. So, in a sense, the unions are to blame for the low starting pay as well. New hires, or those yet to be hired, don't get to vote on contracts, afterall.
But, that said, an across the board requirement for all new hires to have a 1500 hour ATP would definately force companies (and unions) to increase first officer wages once hiring kicks into gear again. It's simple supply and demand. During the hiring spurt a year or so ago I'd say that only about 10% of the new hires had ATPs. That means that the 1500 hour ATP requirement would take 90% of potential applicants out of contention for a year or two, and then I doubt half of those would ever make it to getting an ATP. Companies would have to pay more to compete for a smaller eligible group of pilots. Since every airline would have to do it they could all absorb it equally/raise fares roughly the same.
Am I wrong in this?
Plus, safety is a matter of degrees. I don't think anybody can argue that in general it's not better to have a 1500+ hour new hire pilot whos been around the block than a 250 hour pilot. I think any captain who has flown with 250 hour pilots can tell you that. I'm not saying they are un-safe. Just less safe and in need of more grooming. After a couple years on the job there really isn't much difference, but you still have that year or two interim.