There are plenty of domestic groups opposed to open borders for high-skilled immigrants. Doctors, nurses, and others within the medical profession spring first to mind, and they are incredibly powerful politically. Ditto lawyers or really any other trade that controls its own barrier to entry via the certification process.
And let's not forget software engineers - just see what happens whenever H1-B comes up.
I have never encountered any opposition to high-skill immigration among lawyers. There would be no point--entry into the profession is already gated by the JD/LLM/bar exam requirements. The problem is that getting a greencard requires your employer to prove that they can't find a qualified domestic candidate, which is difficult when large law firms take only 10-15% of the domestic JD graduating class each year and a third to half are unemployed.
No, you're right. Lawyers are protected by their licensing requirements. However the medical profession does protect itself and is opposed to bringing in many foreign born nurses, medical staff, etc.
Lawyers have that nice shield that is the bar exam, but that is also de facto immigration since only ABA accredited schools qualify. So in one sense you're right, the legal profession does not need to lobby against high skilled immigration. However, the reason they don't need to isn't for any moral reason but rather because they can just lock out immigrants through non-legislative means.
And let's not forget software engineers - just see what happens whenever H1-B comes up.