Under an 'open border' policy, things would become worse for everyone, including immigrants. The UK's job market, infrastructure, housing market and social services can only support so many people. A massive influx of unskilled, financially unsupported immigrants (because that is what would happen) would make poverty and unemployment worse. Enormous slums would appear all over the country.
No. A country needs to control who it lets in and how many. It needs to be able to prioritise human capital that would benefit the economy. Things like visas, work permits and study permits actually make sense.