What are the key points against Mass Immigration?

Mass immigration destroys the quality of life of the existing population. It is particularly disastrous in major capital cities, such as Sydney and Melbourne, because that's where most migrants go to in order to join their ethnic communities, and in the worst cases cause enclaves and ghettos.
Negatives include:

• Stagnant or falling wages
• Unaffordable housing
• Less job opportunities
• Humiliating commute times and overcrowding on public transport
• Less business investment in education and training
• Lower productivity, as business can import cheaper wages rather than addressing productivity
• Increased tax burden for infrastructure and welfare
• Lower native fertility as couples both have to work and more expensive to raise children
• Loss of social trust and cohesion from diversity/multiculturalism
• Increased crime, welfare and social service burden
• Discrimination against native population in order to facilitate assimilated migrants
• Degradation of communities
• Loss of public and green spaces
• Environmental destruction from urban sprawl
• Skilled workers taken from other countries, especially poorer countries, hurts those countries
• automation and other technological innovations will radically reduce the need for manual labour. Many jobs that can now be performed by migrants will be redundant.

This is just a summary of the negative impacts of mass immigration. Each point will be elaborated in other blog posts.
Note: we discussed why the elite advocates for mass immigration here: Why are Australia's immigration levels so high when they are disadvantageous to the existing population?