Its not a new selling tax. There is nothing new, just a crackdown on people operating businesses and pretending not to.
If you are selling your own possessions nothing has changed. Therefore it is not annoying that something you have already paid tax on is subject to taxation again, as that is not true.
If you are buying new items to sell for profit then you are a business no matter how small the operation and once turnover reach £1000 you need to declare them and pay any relevant tax on profits. Those who don't buy deliberately to resell are not affected.
I bought something from an eBay seller yesterday, they were marked as a "private seller" but had 50 or so brand new items listed. That is the sort of person HMRC are looking for. That isn't someone who bought something, decided they didn't like it a few months later or it didn't fit and is then reselling it. That is someone deliberately buying extra to sell.