Hm, the term opinion in English has a broader coverage than in German. In German I would say no, it is not an opinion since for most people it is an unreflected urge coming out of the guts. An opinion is something that has been formed at least partly by using brain, information and experience. Not saying those components make that opinion in any way valid, less stupid or reasonable. I just see that an opinion formed by those can be influenced, maybe altered, corrected by fresh experiences or reason. The gut feeling is usually a more deeper rooted sort of fear that is connected to basic instincts and as such less likely to be affected by thinking, reason or experiences.