Torkus If someone has access to my WhatsApp account , can he move move my money? Absolutely, yes!
There is tons of possible bad actors. Paysapp bot (your hosting hosting can be hacked, sms company can be hacked, yourself can be bad actor or hacked) , my sim card company (any bad actor clone my sim card and get access for WhatsApp) , WhatsApp itself. Any actor from this list can move my money without my permission.
Same can't be said for Keybase because with Keybase everything is happening on your client. Keybase is just transferring encrypted messages between peers. When you send XLM on Keybase it just signing a message and sending it to Horizon server. There is no Man-In-The-Middle.