My personal opinion is that large scale immigration is not needed anywhere.
Ditto. As you say, immigrants are going to those countries where the economy is doing well already.
I think a mass immigration (aside scams you mentioned) is deeply connected with globalization of the economy. Hence unholy allice between big businesses and neo-Marxist left ideology. They stopped claiming they are taking side of the working class against exploitation by the big bad bosses and started to defend minorities and that category includes all kid of immigrants. The both sides get what they want from that alliance - big businesses a cheap disposable workforce with few rights, lefties blocks of people (immigrants with a citizenship) voting on them. Win/win for them.
A certain justification for such polices could be a fact that otherwise in the age of globalization many corporations would oft reallocate their firms or rather manufacturing facilities to a foreign country with a cheaper costs of labor. Not to mention a common practice of outsourcings production.
Of course those practices could be prevented by a properly functioned state but as always as long as there is enough cake for most the greed takes precedes over the reason. Hence many countries with a 'liberal' economical policies are riddled with a serious issues and problems with their social, economical and cultural integrity.
Sadly any politically sound solution are shunned by the ideologically obsessed lefties as racist etc.
It will happen anyway;
We got ourselves a believer here. In a destiny as the very least and God knows what else. Here I have thought you are an atheist and rationalist to the fault.