It's useful to have words that distinguish major classes of activity online, even if several types are combined on a given platform. "Messaging", "Chat Rooms", "Streaming", "Forums", "Social Networking", and "Social Media" are all different things. You can quibble about what constitutes the edges of the definitions but they all have different key activities they enable.
If you lump everything together, you fail to understand the necessary nuances to identify the problems let alone solve them.
The key to understanding any given social platform is to understand the proportion of which activity that platform enables. This tells you things like the incentives, constraints, externalities, etc of the platform. Different designs have different effects.