I think the perspective on this will be different due to the generation and experience of each individual. With that being said, I view employment as a mutually beneficial arrangement. You have agreed upon terms that you both found agreeable upon the start of employment and if those terms change for whatever reason then the deal is no longer mutually beneficial and nobody should look down on you for looking for a better deal.
I own a couple small businesses and I know that my employees are there because they feel that they have a good deal, if they find a better deal then I fully expect that they jump at it. I do not believe that they came to work for me to help build my business, they are here to benefit themselves and fund their lives. I in no way view this as a bad thing, it keeps me accountable to ensuring that they are working in a happy environment and getting paid enough to do the job while I still profit as well. I am all about people growing and progressing and if that requires them to leave my business then so be it, why would I dislike seeing a motivated person grow and better themselves? Now I do hope that they give me some kind of warning!
Having this experience, I carry that over to my employment as well. I am a working mariner and I am always trying to progress and seeing what else is available. Having options and researching them is prudent in my mind. You can believe that if the employment arrangement becomes non beneficial on the side of the employer, your employment will be non existent, why not hold yourself to the same standard when the situation is weighted in the opposite way. If you fear your employer may try to cause issues with future employment due to you wanting to change jobs then you should look for the chance to leave ASAP.
Keep in mind, you work to provide for you and yours, not them and theirs. That is simply a byproduct of your labors.
I would list that I am currently employed, you do not want to start off on the wrong foot if you get an interview and tell them that you cannot come in and have to either lie or they find out you were withholding the truth to attempt to make yourself seem more marketable.
Just my opinions. I know many of the older guys that I have worked with in every industry seem to be grateful to have a job like their employer is doing them some kind of favor by employing them and not realizing that they are employed because they are needed.