The first amendment doesn't allow me to have an opinion about scum who despise the American flag and the National anthem?
Does it allow so-called "white nationalists" to march in Charlottesville?
The 1st A. allows you to express whatever feeling you may have about anyone, as long as you do not attack them with lies (calumny can be punished civilly) or violently. Of course people must be careful in how they express themselves, otherwise they can find someone's fist on the end of their nose.
Fortunately the vast number of Americans are civilized, and understand that people such as bripat are not; we who are civilized do not attack or threaten haters like him, we tolerate their disgusting and deplorable behaviors no matter how unsavory they may be.
As to the question above, of course the neo nazi, white nationalists, neo fascists and antifa have the right to express their hate, but not violently; nor can they do so by carrying weapons or wearing masks. They must abide by the necessary permits and restrictions a local community can impose in its efforts to make such events peaceful.