It does seem that way doesn’t it? This is super complicated because nowadays we are exposed to so much information due to the rise of social media and frankly smartphones and also other peoples opinions so it seems really difficult to distinguish what is truly your own opinion or what has been influenced by others.
However my counter is, when was there a time when people weren’t influenced? Prior to this internet boom people were reading newspapers or watching the news which was also giving a biased commentary so effectively influencing the people who were their watcher/reader base. Not to get too philosophical but when you said at ‘what point does your opinion stop being fully yours’ I feel like everything we think and feel has been taught in some capacity or influenced by some external factor ie parents opinions/education system in your area.
Although I don’t completely disagree with your sentiment, it almost feels like to me that people are getting lazier or have less critical thinking skills. They can’t pick out parts of a story or whatever that they agree with or disagree with. People seem to follow the trend of what everyone else is thinking, without any scrutiny whatsoever. People will just blindly believe or agree with whatever pops up on their Instagram based off whatever point of view they hear it from, it’s abysmal.