This seems to be in inappropriate policy as it can cause reputational damage to legitimate businesses and is likely to deter people from doing business with any web site blocked in this way. The onus is surely on Malwarebytes to only block a web site for real dangers rather than blocking sites and putting the onus on web site owners to complain to you in order to get an all clear. You do not even have the courtesy to explain to visitors the real reason for your block.
I object highly to having my web site described as potentially containing scam activity. Have you looked at the legal implications of this as my first reaction would be to sue you for loss of business and damage to reputation? In the case of this particular domain, the web site is just a holding site and not an important commercial site, so damage is minimal. However, I suggest you rapidly change this blanket policy before real damage is done.