There's a difference between INTIMATE CONVERSATION and twisted, demented, disrespectful and rude sex talk.

All relationships are built on intimacy. Yes, even casual relationships.
Relationships are personal interaction between you and at least one other person.
Sometimes they are beneficial and sometimes they are conflicted.

Intimacy is sharing something personal with someone which sets that interaction apart from dealing with strangers.

Being a dating geared website, most define intimacy as sexual but sexual intimacy is but one aspect of intimacy.

Consider this:
Do you walk up to every person you see and share the personal details of your life with them?
I hope not.

Often certain classmates, co-workers and extended family members are excluded from the personal details of your life. No relationship with you is built, no trust is shared.
Other times, you share your personal details with others, trusting them more as your personal relationship strengthens. You become increasingly intimate with them.
Sharing those intimate details with one another is very important to your relationship.

Take dating as an example:
When you meet and greet you don't share all your personal details with that person at first. You slowly release those details as trust builds in that relationship.
As trust builds and time progresses, more and more intimate details are shared, building trust deeper within you two. As trust builds, intimacy increases.

One sure way to end a dating relationship is to try to be more intimate than the trust can tolerate. Its a balancing act.

If the intimacy tries to exceed the trust barrier some people will respond with a general opinion on the subject. When trust is balanced and intimacy is genuine, those same people will respond with specific and personal preferences.
Even in matters concerning sex.

True intimacy in a relationship is vital to the strength of that relationship union.