Let's see, where to begin. Firstly, in the literal text of the First Amendment, the people are given the right to "peaceably assemble." So, as long as there is no violence, people can assemble. Secondly, there is the non-written protections provided the by the "Freedom to Associate." This was created by the Supreme Court in NAACP v. Alabama (1958) when they said that the NAACP was not required to release the names of its members to the Alabama state government. So yes gangs, groups, parties,etc. are all protected under the Constitution. It's their activities that are illegal, but you made it clear you did not want that talked about.
They represent motives, opinions, or ideas. Gangs are the embodiment of freedom of speech itself. I cannot see any way in which the existence of groups is discouraged by laws in an open-minded nation such as the United States of America. This is all based on the assumption that the laws are from the United States of America.
Freedom of assembly is indeed protected by the Constitution, as the the freedom to speak out in support of very unpopular or ever reprehensible things.
However, when gang members actively plot to do illegal activities, laws against conspiracy do in fact apply. But only against those gang members who are actively involved, not against the entire gang itself. Of course, if every member of a gang is actively engaged in planning and/or executing illegal activities, that effectively makes the gang illegal, in that all of its members are potentially up for arrest.
But anyhow, gangs themselves are not and in and of themselves illegal. The things a gang does or plans to do may be, and the members involved in those things can certainly be arrested for it. But gang membership, in and of itself, is not a crime. If it was there'd be a lot more people in jail.
I feel as though the answer is quite simple. Gangs are protected by our right to associate with any group we want. They say a gang's desire is inherently criminal however, that cannot be proven beyond a reasonable doubt. Besides that fact, many gangs were started to help with community service.
It's very simple. An organization can exist to speak and lobby. However, when that organization is responsible for the promotion of illegal activity, then it becomes an illicit organization that is actively promoting conspiracy to commit crimes. That's what gangs are, as they revolve around planning acts of violence and domination.
When someone is deliberately targeting innocent people and breeding criminals in this country that is a violation of the law and should be disbanded. Gangs are worthless street thugs who decided to drop out of school, disrespect their elders, form groups who enjoy being miserable, then have continued to promote their ideas about anarchy and disrespect to everyone who is not them. They should be illegal and the government needs to crack down on them now. They are the real threat to this country.