It is a common alternative conception (misconception) to consider bacteria as dangerous and harmful and so 'bad'. Some very serious diseases are due to bacterial infections, and it is therefore reasonable (from a human-centered viewpoint at least, if not in absolute terms) to class these types of bacteria as 'bad'. However, this only refers to a small minority of types of bacteria. Many bacteria have no direct effects on people, and a good many types are often found in a healthy human gut as part of the gut 'microbiome' that is necessary for proper digestion and a strong immune system.
So, considering bacteria as collectively harmful and 'bad' is akin to considering people as harmful and bad (when some are, and many are not, and others will only be dangerous in specific contexts) or considering rainfall as always a bad thing.
