Of course it is a double tax.  Corporations are 'double-taxed' regularly; revenue sources are revenue sources.  Ask any Legislator, Representative or Senator!  

"The term "double taxation" can also refer to the double taxation of some income or activity. For example, in some jurisdictions, corporate profits are taxed twice, once when earned by the corporation and again when the profits are distributed to shareholders as a dividend or other distribution."

There is all kinds of 'double taxation, both domestically and internationally.

 https://en.wikipedia.org/wiki/Double_taxation

And not all remittances back to Mexico are from illegal aliens; I know many who are legal US citizens who send money South.   So those folks have no worries about being deported.  Mexico, like the US does, can exempt that income from their local taxes.  See the Wiki summary above.