1) It's a non-issue turned into incendiary, racist propaganda
2) Immigrants from the other Americas are here to work, and are largely unskilled; if they are taking jobs from Americans (which I seriously doubt*), who have immense advantages over the immigrants, the only blame to give is to the Americans
3) Workers pay taxes through payroll and consumption. If the employer is not paying the correct payroll taxes, it's their liability and fault and not the immigrants'; proper immigration reform will "legalize" immigrant workers' presence and allow for correct taxation at all levels. (A common argument is "they steal our taxes")
4) Those trafficking goods (guns, drugs, humans) will not be stopped by a stupid wall--the wall is only a show of strength/shame, and nothing more
5) It's a stupid idea and worthless effort when there are so many things worth fixing in America; it only appeals to rich, fat, whites. If you think immigration reform needs to add restrictions, there are reasonable policy measures worth pursuing that aren't worthless like this wall.
*You could argue that systemic bias against black men makes them ineligible for many jobs and immigrants take away their opportunity to work; not sure if this is supportable, but in any case I've not heard it argued that Trump is building his wall to benefit young, black men
