@NoLife1998 You can "disagree" but the evidence disagrees with you. First of all, those aren't the two theories; there are more theories than that. We know bacteria cause disease because of many, many, many experiments showing evidence that this is the case. Plus, the main reason you don't see that second theory is because it's been thoroughly disproven. In the 19th century, scientists such as Louis Pasteur and Robert Koch performed experiments to show this, but it goes back even further than that. We have a lot of knowledge about the intricacies of bacteria, like how they reproduce and can cause immune responses. Also, if bacteria only appear because of disease, then it wouldn't be possible to infect a cell culture by only introducing the bacteria. Viral diseases are typically harder to cure than others because things like antibiotics have no effect on them. That's why we develop antivirals, but effective and safe antivirals are much harder to develop than antibiotics.
You're almost onto something, though, as disease-causing agents do proliferate more successfully when the host's immune system is already compromised by, say, another disease.
Also one more important thing: if you were right, then vaccines wouldn't have any effect. But they do.
If you're interested, look up the experiments Louis Pasteur did regarding germ theory. Also, look up Koch's postulates and how he devised them, plus the alterations made later to them.