As fraudulent as this practice maybe, it can't really be stop because of the unregulated design of bitcoin. It is also impossible to detect insider trading and even if you were caught its really hard to prosecute those who practice it. So for me, since its really hard to detect it, at least it should not be ban IMHO.
But in the point of a investor, I will lost confidence in the market unless I know that I'm competing on a level playing field. I guess we need to be immune in this kind of practice, however, I still believed that we needed it specially in the crypto market.
I personally don't think that insider trading is inherently wrong or should be illegal - this is not like stealing money from someones pockets, because people voluntarily agree to participate in open market. If there is demand from people for regulation (because they view such practices as fraudulent), it is possible to create voluntary regulation inside Bitcoin economy - i.e. exchanges setting up their own rules for the benefit of the market and not because the government told them. The question is, do people really want it, or maybe everyone is okay with totally unregulated markets?
Insider trading has always been a potent part of the game and even in the fiat world that can be tracked not to talk of the crypto world where anonymity is the other of business and those people are not the only ones guilty, you didn't mention the admin sites of pump groups who has a lot of followers and knows before hand the coin to be pumped even before announcing to the group that's also an element or insider trading when looked at intuitively.
Pump groups are not the same as insider trading, since they only influence price via market means. In traditional markets this treated as separate form of fraud.