Migrants undergo a lot of harship as a result of being forced to enter countries illegally. There are many cases of torture and robbery at the hands of people smugglers, arduous journeys across seas and deserts, abuse at the hands of police and citizens in their host countries amongst many other physical and mental hardships.There are many deaths.
In the year 2017, there were over 6000 officially recorded deaths of people who perished in the intentional process of migrating towards a country different from their country of residence. (1) The actual number of deaths is expected to be much higher. This is a direct result of border regulations which prevent people from crossing borders legally. Opening the borders would reduce the number of people who have to die and suffer as a result of being forced to enter countries via illegal routes.
It is also possible that open borders will increase the number of immigrants choosing to relocate, and that the number of crimes committed against them will increase. It is also likely that the people that are committing these crimes will also immigrate to the same countries, and commit crimes there, both against the vulnerable immigrants as well as the vulnerable citizens of origin. It is also possible that policing in the destination country will become over taxed, resulting in ineffective policing, and result in increase death and suffering to both immigrants and the citizens of origin.
Migration through illegal routes causes death and suffering. Opening the borders would stop migration through illegal routes. Therefore opening the borders would stop death and suffering through illegal routes.
Rejecting the premises
The premise contains at least one logical fallacy. People are not forced to immigrate, it is a choice. Open borders will not stop people from abusing vulnerable immigrants.