On the one hand, as an example, the company that is presently my main source of consulting work has engineers and others from many countries, here legally, and they came here as highly skilled and valuable people, hired for particular skills and knowledge. My own wife is a legal immigrant, again well educated, skilled, etc. These people are net gains in many ways.
However...
A typical illegal alien & their family are a net drain on gov’t resources, not a net gain. And most live VERY frugally, unless they are in the drug trade. Even many legals (e.g., migrant workers) get by on what I would estimate are 1/3 the expenses of an average middle class US citizen. Food IS still a significant expenditure, but food is low or no-taxed in many states, not (directly) Federally taxed, and due to gov’t subsidies (another drain), while many of us complain, food is still “pretty cheap” compared to most other commodities, unless you insist on lots of beef or higher-end seafood in your diet. Transportation is often by group — “10 people in an old minivan” is not as much of a stereotype / caricature as you might think. Meanwhile, money pours out of the country.
These people sure aren’t out there buying new bass boats.
As for abortion, there is some truth to what you say, but why do most women have abortions? It’s economic pressure. Some may just not want the bother of a child, but again more typically, the woman simply doesn’t think she can afford the child. If she could, voila: Lots more consumption.
Direct observation, on all sides of it, for many years. Maybe you should try it.
And since our government is effectively bankrupt, even the "drain" you describe is being financed largely through cheap loans from creditors anyway.
We are like a farmer who has 4,000 acres of land but can't run his farm profitably. He figures he can get by for the last 40 years of his life by selling off 100 acres of land every year just to cover his operating expenses. He'll do OK, but there won't be any farm left by the time he dies.