Inded. It would help if everyone stopped denying that Tumblr and similar social media platforms have done more to drive this than any other factor.
In a lot of cases, being able to connect with communities of likeminded people means getting to express and discover one's true self and core identity.
In many others, identities are adopted and discarded along with the online communities, or the communities suck in people into de facto cults.
The subconscious element is the impact of constant signals and advertising from reading or watching repetitive content. One example being the message conveyed to girls and women by constantly seeing images of slim women - that will have an effect on their body image and can cause dysmorphia, anorexia, etc. Another example is the effects of porn on male sexual behaviours, with previously marginal sexual practices becoming mainstream by dint of sheer repetition and labelling/marketing. These things might not rise to the level of identities, but in some cases overlap with them.