Ok, what if this person were a thug and he advocates for a "thug life" (as an arbitrary example, a gangsta rapper)? And let's say he committed a lot of crime and physical harm to other people?
Would you issue the same behavior towards him? Would you be very vocal about it?
On the surface, this seems like a silly example - it doesn't compare in practice. However, if you honestly, in good faith, think that it does, you absolutely should make an effort to form that argument.
I believe that what he is trying to say is that, even though the lyrics are about killing people, selling drugs and so, nobody bans their music and they have the right to express themselves.
Posting the most offensive examples of gangster rap lyrics to Facebook or Twitter could easily get you banned or at least flagged/shadow-banned if the songs were about killing people, contained a lot of misogyny, etc. Uncensored gangster rap would definitely violate TOS for a lot of these platforms and would probably get auto-banned by bots. A lot of this music gets flagged as 21+ only on YouTube. Many businesses ban it on premise, and many record companies won't publish it. That's part of why the really extreme stuff tends to have its own labels, stations, channels, sites, etc.
You're allowed to listen to it in private of course, just like you are allowed to read or listen to any racist material you want in private. There are loads of web sites that cater specifically to these circles, and even entire alternative social networks. Like the most violent and offensive gangster rap, it has its own safe spaces and is available to anyone who wants it.
Would you issue the same behavior towards him? Would you be very vocal about it?