There's so much here, it's hard to pick a starting point. :)
I guess I'll start with where we agree.
The current process to immigrate lawfully into this country is a labyrinth, not a straight line. If making it possible for people to go through the process more quickly and efficiently were the focus of immigration reform, some issues we have would dwindle or be eliminated.
The cost of deportation you describe is excessive and unnecessary. I believe enforcing current immigration law would cause people to leave. I've seen it happen before, I don't know why it wouldn't happen again.
A sudden loss of a labor force would create a huge problem in any particular industry.
Where I struggle to agree:
I believe in a nation of laws. Immigration in this country and virtually every other country (to account for a handful who may not) is governed by law. In legal terms, immigration is more than simply moving across borders anytime you want, for any reason, valid or otherwise. The process stinks, but there is a process.
There are exceptions made for people who live in countries where they are persecuted, oppressed and the like. They still have to go through the process, too.
Coming here unlawfully because you want to make a better life for yourself and your family would hold more weight if there weren't so many turning around and sending their earnings to family living outside the country, while in many cases receiving assistance for housing, food, health care, etc., all things which are not universal legal to receive.
Who hasn't heard of "jobs that Americans won't do?" Yes, most farm labor does not earn a living wage, and a lot of it is backbreaking. But I did it as a 17-18 year old 34 years ago. There's an entire underutilized teenage workforce that doesn't need a living wage and could stand to learn the value of hard work.
There are still wage laws governing the minimum employers must pay. If they are circumventing that to keep labor costs low, it doesn't matter what the legal status is of the worker. The company is in violation of wage laws. If it's so rampantly done so as to affect all food/agricultural prices, we have a bigger problem than just keeping prices down through the use of cheap labor.
Martin Luther King, Jr fought against laws that violated basic human rights. He disobeyed and often went to jail for it. Others died because of it.
The ability to go wherever you want whenever you want, regardless of the borders or the laws governing them is a lofty idea, and something I could get behind if it were universally extended and reciprocated. But whether such an ideal rises to the level of a human right is still under debate. And while it is, I believe in following the law.
I agree with you that employers must pay at least the minimum wage to its employee's, and this should be true regardless of legal status of the workers, and I also agree with you that teenagers and young adults today are just to be paid the minimum wage. Actually, this is already true in our economy with individuals under 25 making up for around half of all minimum wage workers. It would be unreasonable to pay, for example a farm worker significantly over the minimum wage where their job entails no specific training or education.
But I also believe that growers today enforce a sort of plantation style mindset where they prefer to hire large amounts of illegal immigrants over investing in mechanization and other methods that would lower their labor elasticity. While I cant criticize them for how they run their business, since it makes sense to keep labor costs low instead of investigating in machinery. The reason I stated Martin Luther King Jr. was because there are already various examples of human right abuses by growers. Since illegal labor is dispensable and easily recycled, it paves the way for growers to harass and mistreat laborers, making them feel superior, while the laborer inferior. HRW posted a very good article about this if your interested in reading it.
https://www.hrw.org/news/2012/05/15/us-sexual-violence-harassment-immigrant-farmworkers
A good step the government should take in my opinion is introducing subsidizes to these growers so they can raise their efficiency and stop the steady stream of immigrants they hire. As you said today's policies are inefficient, maybe by cutting the demand of immigrants by technology instead of raising wages to attract domestic workers would be a better solution.
However it would best work out, we're in agreement that the current arrangement isn't truly in the best interest of the undocumented immigrants due to the reasons you cited, and really, if the growers or their supervising employees are abusive on top of breaking the law (in all sorts of ways), the problem needs to be resolved on that level, too.
I'm not particularly fond of subsidies, though I know it's hard for much of the agriculture sector to otherwise make a profit and keep prices low, but if it could be used to incentivize good behavior (hiring documented immigrants/citizens, or going mechanized), than that would be better than the worst happening now.
Great topic and discussion. Thank you!