I think the reason of why people are giving such neutral or negative tags like that because they just want to leave a sign or warn to other users. If they didn't leave the tags on the accounts, where do you think they can leave that? creating a new thread in Reputation thread seems not be the best solution since people will also have something to say e.g. there's no proof, don't suspect every user account.
If you ask everything is need a proof, I can give a counter argument where a ponzi scheme project offer 10% per day.We're just suspect it's scam since they offer unrealistic return, but there's no proof of they have scam anyone.
Everyone is obviously in control of their own trust list and are able to tag at will, but if you do not have enough proof and are looking for opinions IMO best tohave a discussion in a thread and see what the community digs up before tagging.
It's like someone should leave the tags based on other DT members' opinions, not based on his own judgement.