This is the exact same scenario when McAfee is just shilling new projects and different coins/token in his twitter account.

He might tweeting something but he can freely do it since we have the freedom to do it. The problem lies with the investors not with Elon Musk at all. He can say that Ripple would pump in the next week and investors will not react into it. He can shill anything but it is the decision of the investor whether they will listen to him or not.

You can say it bad but see the other side of it too. Losing in trading is inevitable especially when you got FOMO'ed with things like this but on the other hand, there are traders who are winning because of these tweets. He can say anything but it will depend on the investors if they will react into it.