Same way any other website with user-generated content deals with it. The website has broad immunity as a platform, but is expected to take down content that would be illegal when notified.

Random people on the Internet have been at it long enough that there is plenty of precedent to establish that you can safely host a platform. But then again, I am not a lawyer, I am not your lawyer, and for legal reasons this is not the legal definition of legal advice, etc.