Can job hopping be justified (please read details)

I’m talking about a situation where maybe you were laid off and had to take a job well out of your normal career field in order to live. You have realized during a certain amount of time on the job, and maybe after a negative evaluation or two, that this line of work is not for you and you know that you’re not going to able to perform better within the time frame the company expects you to. You also know this company will terminate your employment if you don’t perform according to their standards. You desperately try to find another job in order to give such a company a two week notice in order to avoid putting down that you were terminated from a job on future applications.

Another scenario I can think of is where I left a hellish low paying job in order to try something new and better paying, only to find that I bit off more than I could chew. You have no way of knowing what a work experience will be like until you actually work there.

I’m asking this question because I’ve been forced to take jobs that I didn’t necessarily want to, but had to due to things like bills and living expenses, I mean you have to work to live. This has also put me in an odd predicament where I’ve worked at many jobs within the past seven years, where I average about six months to two years at each place. I did work at three previous companies for a while where I was actually working in my career field, but when the last place closed down I’ve struggled with my jobs ever since. I always give the company a two week notice prior to leaving. It seems that many employers have used my job hopping against me, where the person/s interviewing had pretty much made this clear to me during the job interview.

Not just confining this question to my own experiences, I’m asking two questions here. I wanted to know why job hopping is looked down upon considering the nature of the job market, and the natural urge most people have for wanting to better themselves. Moreover, I’ve noticed that many white collar workers I’ve known, and including those in management positions change companies frequently too, even more so than myself and always seem to get job offers. Is job hopping looked down upon more if you’re a blue collar vs a white collar worker, or is it viewed the same in the eyes of most employers?