Fame, curiosity, boredom.
This three are the most common causes of 'Ghost Hunting' tours.
When somebody is interested in something, what do they do? - Reading about the topic, listening about the topic, trying to understand it more, and when you feel like you can't squeeze out more knowledge / information of these which would satisfy your hunger, you'll pick your stuffs up and go out, to seek for the subject 'face to face'.
Unfortunately, the chance that you can disturb spirits / or literally, any existing being / is there, you can't avoid it. You can disturb animals in a forest when you walk there, simply because of your presence, or even other people. You can also disturb entities / spirits even on different realms as you pass through and there is a chance that you summon / call who have no mood nor interest to interact you, as well. What you can do is to show respect towards them, and if it turns out you disturbing any being, you would leave silently.
They are not "owners" of the properties where they are spending "time" - neither any type of physical body -, and they can also process the effect of getting disturbed, it is not something which will cause them eternal trauma, but a proper respect from the beginning is really-really the core of the whole thing, and the will to understand if they really don't want you to be there.
We can safely say that if you interested in seeking for this knowledge and experience, you might risk to disturb spirits, but this is a part of the life. If you use the knowledge for good, and handle them anyways respectfully, and know the lines, you might cause less trouble for them and yourself. The way how some people behaving in haunted places are very disrespectful, that is for sure, and the way how talk to the spirits. They can sense your intent, and how you see them, feel towards them too, you can't fool them that easily.
Also, having "visitors" can give them a chance to get some energy out of their attention, and this is an another reason why they might try to interact with them and the environment. It is a sign, which can mean many things, but can only be understood if the team have the intent and care about it.
Ghost Hunting can be an interesting, exciting and chilling thing, but of course, it can be very dangerous. Not just because of the possibility that you'll run into methead, drug dealers, aggressive homeless people or wild animals, but because, as you said, spirits can be very violent and powerful, and can ruin your life. They can either just try and chase you away, or even attach themselves to you, and follow you back home, for various reasons.
I won't lie, I plan to do these tours myself too, but I don't plan to share these online in a publick circle for fame or attention, and for me it would be more about potentially helping the souls out if they're stuck between the two dimension and can't move forward, either because a cause of death or because of the dimension gate which they used to come throught, closed and so they need help to find a way to get back.
I'd say, that having a medium, a magickian in a 'Ghost Hunter' team can be very useful, and should be there if you really want to take this thing serious, or even you should take the effort and time to open your senses again, and be able to communicate with them too, not only using devices - whichs' presence are also understandable and can be good indicators, but these will not always guarantee the evidence collection -.
