Work Ethic VS Free Agent

Recently I got a better job offer. The offer is good so I tempted to leave. Later when I resign, my current company counter offer me with a better salary. So I told the other company about the offer and I tell them I need some time to re-consider. The other company tell me that they think that I am not ethical considering I have signed the letter offer with them but still thinking of the counter offer. I was thinking about this. How ethical is consider ethical? Nowadays if company need you they will pay you good salary to work for them. Once they don't need you, they will retrench you anytime. Does that mean ethic? There is no such things as job security nowadays. Retrenchment can happens anytime, anywhere. All the while I consider myself as a free agent in the job market. I am selling my expertise and services to my employer where they pay me salary and benefits. I do my best for them. But on the other hand I do my best for myself. I work hard to create my value and I work hard to get better pays. I create value by do more than expectation and increase my responsibility. I am responsible for my own career path and what I will be getting. I'm not sure other people thinks like this but this may be the characteristic of Generation X (1965-1981). According to Glenn Shepard (in his book How to Be the Employee Your Company Can't Live Withtout-18 Ways to Become Indispensable),'Generation X distrusts institutions and feels little loyalty to employers. They see themselves as free agents in the job market and consider it acceptable to change jobs more frequently than previous generations.'