You can build bots for Whatsapp. There used to be lots of libraries and samples on github before the DCMA takedown. There were libraries in C/C++, PHP, JS and Python.
Here in Brazil we do have Whatsapp and SMS spam. Whatsapp spam is rare but it happens and it will only grow.
Of course you _can_ but whatsapp is actively trying to prevent you from building those bots, and they may succeed well enough in their goal to have a measurable impact.
It is easy for us to say that a growth of whatsapp spam is inevitable but I would bet a key part of whatsapp strategy is to take that down to as close to nothing as possible. In comparison on fb and instagram spam is embraced. I think that is part of the reason why we see whatsapp taking a different direction than other seemingly similar social networking companies.
Here in Brazil we do have Whatsapp and SMS spam. Whatsapp spam is rare but it happens and it will only grow.