I get force fetching, but allow me to make a short story long. I'll start by admitting that I don't have the highest standards for my dog(s). As long as they're usually well-behaved & do what I need them to do in the field, I'm happy. Field requirements include stay reasonably close, find birds, flush them, and don't lose them.
I got my first springer Walt in 2002. He was 5 months old on opening day, and it didn't take him long to get the hang of roosters real well. About 2/3 through the season, he started retrieving on his own, and we never looked back. I never taught him anything other than basic obedience. To me, he was a phenomenal dog.
I got back-up springer Buzz in 2012. He picked up hunting real well that fall, but regardless of which dog got to a downed bird first, Walt (a pretty domineering dog) ALWAYS retrieved it. Of course, both dogs would come to me, Walt with the bird, & I'd praise them both big time. Then in Sept. 2013, Walt died. The 2013 season without him started out really frustrating. Buzz had no problem finding plenty of birds & getting them in the air, but we were losing a few, which I wasn't used to at all. I finally realized he was finding the dead birds just fine, but he'd sit down by them & just stay there. I had to first find the dog, and there I'd find the rooster. So then I started making sure I got to the spot somewhat quickly too, so if the bird was giving Buzz problems, I could grab it. This went on for 3 seasons. We shot plenty of birds, and lost VERY few. That became good enough because our hunts were successful & I praised Buzz every time he didn't retrieve a bird. I firmly believe I'd taught him not to pick up birds.
Meanwhile, everyone's telling me I have to force fetch him, which I admittedly didn't want to commit to. I just figured there had to be an easier, more fun way to get my dog to retrieve. I tried wings, which he initially shied away from. I tried full birds, which he'd pick up if he had to, but always acted like he was scared to do it - that he was doing something wrong, even if he received tons of praise. He'd fetch pretty much anything, as long as it wasn't in an actual hunting situation. In 4 seasons, he'd put exactly zero roosters in his mouth. I'd had to strip down to retrieve a couple birds in sloughs (warm-weather days); gone through ice as he happily sat by his prize; all manner of things to make the final pick-up & put birds in the bag.
One of Buzz's true loves is flying off the dock into the lake to fetch the bumper. He'd do it 24/7/365 if he could. 3 weeks ago, during our residents only season (public land), I shot a young bird as we hunted around the edge of a large pond/slough. It finally dawned on me, "What if I THREW this thing in the water?" After finishing the area, I chucked that bird in the water. He bounded out there, thought about it a while, and after a bit of encouragement, brought it back. We did this probably 15 times, in the water, the weeds, the cattails, everywhere. He had an absolute BLAST! The next 2 birds, he considered picking up, but just didn't. However, I threw them in the weeds & he'd go get them. The following weekend, after some begging on my part, he retrieved his first rooster on his own. Then 2 more with a little pleading. Then a couple withOUT begging him to do it. This past weekend he retrieved 6 roosters completely on his own, without any encouragement on my part. He's doing it very happily & receives tons of praise. I anticipate it will become more & more fun for him & that the retrieves will get a little more aggressive. He hasn't made a TRUE believer out of me quite yet, but I firmly believe we've turned a major corner.
Point being, there's no doubt in my mind that my first dog Walt & I inadvertently taught Buzz not to pick up birds. I know there's a place for force fetch, but I also think that if your main goal is just to get a dog to retrieve birds, there might be another way.