I will respond to each of your statements. I dont mean to cause offence by arguing what you say, but you asked about others opinion so here is mine.
POINT 1: Think how big the entire universe is. All those stars at night might have life going round them just like us. Count them on a clear night, do you really think we were the only life in the entire universe?
Also think they might be visiting Earth before they fly past to go and visit someplace else. They just stop here to observe and prehaps make notes on us. We may be someones experiment and they keep coming back to see how it is going. Just one example I can give of many. (See my other answer on 15th Feb for another answer).
POINT 2: Not all craft are the same. Although they may look advanced in our eyes, if you took alien spacecraft and their owners and asked them what they thought of each others vehicle, they might say "Well their craft is slow compared to ours, and its not as advanced as ours." It may not be the same technology, again, it just looks advanced in our eyes.
POINT 3: Prehaps they dont want to disturb our way of life and want to let us develop on our own. There has been contact with certain individuals, but they havent come and announced "we are here", so you have this speculation (which is why I am typing to you now). This you could say means our way of life hasnt been disturbed but they can still make contact with people. How do you know that governments haven't met aliens and discussed things with them.
POINT 4: Well, I cannot give you a true answer, only a thought on why they come here. We could be an experiment and they wish to keep tabs on us to see how things are progressing.
Another point is they want to help us by sharing their probelms and experiences with us to save us from problems they have had to encounter. Nuclear weapons may upset aliens and so they want to prevent us from causing ourselves problems and them too.
Prehaps 'aliens' were from Earth but became more technically and socially advanced and left Earth to explore pastures new and now return to see whats happening to those they left behind.
There are many more, but I think I made the points clear enough. If I havent please do tell.