First, its very unlikely it would need to put into effect...the threat is sufficient.
Second, if it is enacted there are many ways to mitigate the impact on the public.
Third, I'm happy to pay 10 cents extra for bananas and plantains if it means the border is secure.
This is how negotiations are done. You start with harsh terms, and walk it back...though admittedly, there are times you have to set an example. But remember who holds nearly ALL of the leverage here...and it ain't Mexico.
You'll have a shock if you think it is just going to be ten cents on a pound of bananas. But, let's use the importation of bananas as an example jsut to make this simple.
In addition to the tax directly on the imported bananas, you have to account for the transportation. Many of the parts in the trucks that bring the bananas are made in Mexico. A large percentage of our gas is also refined in Mexico. You just have shot up your transportation expenses for said bananas as well. Then you have the truck drivers. They will be getting hit with all the extra expenses, so manpower costs will go up. (he buys goods just like you and if his paycheck has less purchasing power, he'll demand more..) Then, you have the machinery used in the factories to clean and sort the bananas, their expenses now go up. Your grocery store refrigators, more expenses going up... and so on and so on and so on...
When you have artificial manipulation in the markets, such as sudden import taxes like this, it effects far more than just the one product you think of. It makes waves through many other related products and goods.
It is the same reason the ACA is killing the healthcare market place and making things more expensive.