It is often considered that as we pass adolescence, we become old enough to decide for ourselves, therefore we cease to be influenced by social pressure and we never follow the crowd; supposedly only "weak" people follow the crowd. This argument is often used to dismiss the idea that any form of social pressure can be a factor in people's decisions, so if a person makes a negative choice the person gets 100% of the blame, end of story.
To my mind, that idea is flawed. Yes, we make decisions for ourselves, but social factors attach 'strings' to our decisions. For example, if I have a choice between X and Y, but the real choice is "choose X and be rejected, or choose Y and be accepted", if I then choose Y, it does not follow that the external social 'strings' (rejection vs acceptance) didn't influence my decision. Also, saying that we are all influenced by society is not necessarily a criticism; if we were never influenced, we would never learn from anyone.
I'd agree that only "weak" people are easily influenced into making negative decisions, but even strong-minded people can be swayed, if strong enough social 'strings' are applied to their decision making processes. It's probably fair to say that, as a general rule, the more social pressure is required to 'sway' someone, the stronger the person, but there's no such thing as a person with an infinite 'stubborn-ness' threshold.
So what sorts of social pressure influence us? It ranges across a variety of spectrums, from individual peer pressure, manipulation and outright bullying, to social norms representing codes of behaviour or belief that are generally accepted without question, and where it is often socially unacceptable to deviate from them. In larger-scale forms, people are often also influenced by the weight of consensus (if everyone believes/does it, it must surely be 'right'!)
Even the "we are who we are" concept cannot accurately be used to dismiss the influences of social pressure. People learn to conform from an early age, particularly in the school years, and this helps to mould our personalities as we get older. In all of these cases, I include myself under this bracket; I like to think of myself as an independent thinker but I, too, can be 'swayed' given enough pressure in that direction.
I think it's important that this preconception is challenged, because in reality, many problems do have social pressure as a root factor. At a small-scale level, people can manipulate and bully others into making negative decisions; it makes no sense to me that the bully should be absolved of all responsibility on the grounds that "a strong-minded person could withstand an infinitely high amount of social pressure". This is relevant to many issues, such as school bullying, employer abuse of working hours (manipulating employees into 'wanting' to work 70 hours per week) and friendship issues (if a jealous third party tries to break apart a friendship, a 'true' friend is expected to withstand an infinite amount of manipulation, such that the third party never gets any of the blame and the friend can never get any support)
Negative social norms also contribute; people often make negative decisions based on the blind acceptance of codes of belief or behaviour that are passed down the generations. For instance, take discrimination against women in the early 1900s; I'm pretty certain that the campaigners had to tackle and break down various social norms before they could make any significant headway against the issue. Accepting that people made their own decisions, and absolving social norms of any responsibility, would almost have been tatamount to resignation, and a 'that's life' attitude to the sexism.
So, we need to recognise that social pressure can be a factor- in order to enable it to be addressed!