This goes mostly for younger people, but I've heard plenty of talk about women especially, who force their partners to completely respect their boundaries and justify the lack of sexual activities with, "You don't need it." You don't physically need it, but in order to be satisfied, yes, you do.
Why is it that it's okay for that same person to completely disrespect their partner's desires?

No, forcing someone into sexual activity is absolutely not okay.
But, as far as I'm concerned, forcing someone out of sexual activity isn't okay either.
It may not be on the same level as forced sexual activity, but in a relationship it's still pretty wrong.

Your partner should be able to fulfill your needs. If you need boundaries, you need a partner who has similar boundaries. If you want lots of sexual activity, you need a partner who wants the same.

The common argument against this is, "Well, if you love someone..."
Yes, if you love someone you need to respect them.
But, this respect goes for their boundaries, and their desires.
If you love someone, don't you want to meet their needs, and wouldn't you hope that they would want to meet your needs?

Don't go out and do something you really don't want to do, go ahead and stay within your comfort level, but you may want to figure out if your partner's wants and boundaries fall into that comfort level.

One thing I've personally noticed about dating, especially at younger ages is that people will automatically jump into a relationship with anyone they like, even if it's so incredibly obvious that it won't work out. I think this eagerness to create a relationship is what leads to so many failed ones.
People seem to have a hard time stopping their pattering hearts, and raging hormones for a second to think about what may happen if they do get into a relationship with someone. In my experience, they're too overwhelmed with the wonderful feelings of love, lust, and excitement that they forgot to look for some of the fundamentals of a good, healthy relationship.
Communication: One of the absolute necessities for a good relationship is communication. Communication is the glue that holds all of the aspects of a relationship together. If you lack in communication skills, maybe you should work on those a little bit more before you decide to go steady and exclusive. Also ask yourself about lying. Do you lie to this person often, have you before, what were the lies about? Have they lied to you, etc?
Trust: Trusting your partner, potential or not, is a must. If you don't trust your partner, or if they don't trust you, usually accusations and high insecurities arise. You'll feel bad about yourself, and suspicious of your partner, or vice versa. If there's a lack of trust, stay away from a relationship.
The Ability to Get Along: Ask yourself how you function as good friends. How often do you argue/bicker with this person? What do you argue about if you do? If you don't argue, why don't you? And things like that. If you find that your potential mate is a common opponent in arguments, rethink a relationship.
Love*: Yes, love. This is pretty self explanatory. If you don't love this person, and they don't love you, why are you in a relationship with them? 
*Substitue the word love for any other word you want to call being interested in early, or potential relationships.
Sexual Compatibility: Even if you aren't sexually active, and don't want to be, your partner needs to want basically the same thing. If you choose to be abstinent, and your partner wants to be sexually active, there will be tension. You also can't have widely different turn-ons and offs. If you're into pain and completely turned off by stereotypical romance, and your partner is completely the opposite, you will not be satisfied.

If you're having issues with relationships working out, maybe it's because you're not thinking about how a relationship may work out between you and the person you're interested in.
So, just because you like someone, or even love someone, doesn't mean that a relationship will work out for you.
Relationships are just like houseplants. You can't substitute light for fertilizer, in the same way that you can't substitute love for communication, or trust for sexual compatibility, and so on.