I've explained my opinion. If you want me to do it again, even though you've said it (and everyone else's) is irelevant to you, here goes.
A number of poster who have had a treadmill themselves, or who have lived under one, told you YABU. Others raised new concerns.
My opinion of the original question, as I said in my first post, was formed through reading the posts here. If you'd asked me two days ago, I'd have said I had no idea, and certainly didn't know treadmills weighed that much, made that much noise, or irritated people's neighbours so often. Now I have made an opinion, by reading the information and views presented by others. Which I would have thought would be a good strategy for the person actually asking the question, too.
I also ventured to say that your neighbours may be as ignorant of treadmill realities as myself. If my upstairs neighbour asked me, two days ago, if I would mind if they got a treadmill, I would have replied just like your own neighbours did. Because I wouldn't understand what I was actually agreeing to.
But if the person asking has more knowledge and actually knows there are reasons why it is inconsiderate and un-neighbourly (for instance, they suspected they might be being un-neighbourly by doing it, asked around, and had numerous replies telling them it would in fact be un-neighbourly!), I would think it was pretty unpleasant of them to write off those concerns because after all, I'd said it was OK.
And yes, Pipbin has it. Because you have invited opinion, yet not only refused to listen to it, but said that everyone else's opinion is not valid because they are not you or your neighbour and are not familiar with the lifestyle lead by everyone in question. and But you didn't seem to use anyone's opinion as any part of your decision making process.