I agree, there will be nothing to prevent hatchery fish from moving upstream. But the affect on wild fish is not the reason those barriers were installed. The were installed to prevent fish from moving upstream into the water source for the hatchery, thereby reducing the possibility of introducing diseases into the hatchery.

All migratory fish (both hatchery and wild) are loaded with naturally occuring diseases. Under normal circumstances, these diseases aren't a problem for fish in the stream. But when these diseases get into the water supply for a hatchery, they infect the eggs and young fish. Under hatchery conditions (crowding, stress) these diseases can wipe out a year class of fish, or perhaps the entire hatcery. That's not good. If these barriers continue to come down, disease problems will occur. That's the downside of removing barriers at hatcheries.