The problem is that "we" need people to do the dirty jobs we don't want to; wait tables, mop floors, clean toilets, change diapers for the elderly, and so on. Most of those jobs come with a fair deal of risk of physical injury or verbal abuse and the pay is usually crap. What makes you think that migrants would be content with those jobs when we refuse to do them ourselves?
Besides, in large parts of Europe, Eastern Europeans have already grabbed most of the decent jobs available to foreigners. The millions of Ukrainians currently fleeing the war will grab what's left once they start settling in and become available on the job market. In that situation, importing a vast amount of African youth into several generations (at least) of low social status is both cruel and unneccesary.
There's definitely reason to revisit the way we look on migration, but flooding the market with cheap labour is not going to solve anything. We need to reform the labour market and automate the jobs that cannot be made into decent ways of making a living. Other shitty jobs will need to have working conditions improved until the jobs themselves are worth taking.