Is it a good decision to think of a PhD and a future academic career in an area which I ended up leaving my previous adviser in? Do professors hold grudges and vent it out later professionally as they become big shots?

Some people (not just professors!) hold grudges, others do not. If you have passion for the research area, then continue in it. Although your former advisor might not be your supporter, there will be other people working in the area and if you're good, you'll be recognized. Two stories: (1) When I was a young assistant professor, I realized that the same person -- THE expert in my field -- was being asked to review many of my articles and grant proposals. This was in the days of word-processors, but pre-widespread email and web. This individual happened to have a very distinctive type-font on the printer s/he used, and since I'd corresponded directly with the person, I recognized the font on the reviews I got. The reviews were actually pretty good, and very useful. But I was afraid the person might be getting tired of getting my stuff to review, so I put the person's name down on the list of people I'd prefer NOT to be asked to review my material. More than 25 years later, I'm good friends with the person. (2) I had a student who I didn't think was doing well. I really questioned whether the student had the "right stuff" to be a scholar. I told the student my opinion, and eventually counseled the person to leave our program. Instead, the student found another faculty member in our program to be the supervisor. Within a year, the student had published a single-authored paper in the most prestigious journal in our field. The student did an excellent thesis and in a highly competitive job market got one of the few good jobs available. Moral: Advisors aren't always right, and some of them know it.

A2A The quick answers: Professors are no more likely to hold grudges than any other people. No one person holds a "monopoly" on an intellectual topic. You should study what you love. The central question you asked is how to try to mend fences with your former advisor. I'd suggest sending them a very brief email containing the following pieces: (1) Say that first and foremost you are writing to apologize for (immature behavior? being unreliable? poor communication?). Keep this short and make it a pure apology; do not offer any excuses or qualifiers. Say that you are trying to do better in that area. (2) Mention that you have decided to make a fresh start in the field with a new advisor because you love the field. (3) Ask for a small piece of professional advice. Make it something that would genuinely be useful for you to know and would be easy for them to answer quickly. For instance, you could ask for a recommendation of a review article to read in their field or what advanced course would be useful to take next. This note signals that you'd like to be on a collegial footing. People usually don't mind receiving an apology. Asking for advice shows respect for their opinion. If the prof answers kindly, you are all set; you can stay in touch occasionally. If they answer brusquely or don't answer, you can conclude they aren't very interested in staying in contact. It's very unlikely they'd bother sending a rude answer; if they did, you'd know to steer clear.

People can be difficult, and, as noted by others, are as likely or not to hold grudges as anyone else.  But you are likely to run into people with strong disagreements in your field at one point or another anyway.  Some will behave with integrity, and make their criticisms cleanly and openly.  Others may pull dirty tricks like sitting a a paper to review, or spiking it gratuitously.  On the other hand you will meet great people and will have the pleasure of sharing the excitement of interesting research and questions with people whose knowledge and judgment you treasure.  If research and scholarship draw you, nothing should keep you from pursuing it.  You need it in your life.

Thank you, Professor Marcia Bates for your support. I appreciate it.