Well without NASA as a species we are fucked. It is the largest most advanced space faring organization we have. Here I will outline every single reason why anybody who says defund NASA is a deranged lunatic. Let's begin shall we?

What has NASA done for us?

NASA has helped The United States and the entire world grow more technologically advanced in many different ways.

Without NASA we would have far less satellites.

NASA has put almost every single satellite into orbit and at a reduced price.
What does this do? It makes it far easier for businesses to get satellites which means they can be used for more things. We are able to track the weather, increase the range of TV and any other signal and make it possible to track where an object is (GPS).

The "free market" can't provide this service for that low a price and help business in the same way. This means that communications and innovation would be lowered.

NASA has helped create a ton of technology that has changed the world. This is a list of technology they have created or technology their inventions has been used in.

• Light-Emitting Diodes (LEDs) (invention)
• Infrared Ear Thermometers (their tech was used directly in invention)
• Artificial Limbs ( Tech makes them far more functional)
• Ventricular Assist Device (collaboration)
• Anti-Icing Systems (invention saves many lives used from sidewalks to planes.)
• Highway groves ( invention)
• Improved Radial Tires ( side invention used for rovers and material is now used in them)
• A chemical detector ( it can sense them along it's entire length, used by government to detect chemical warfare agents. invention)
• Major breakthroughs in video enhancement. (They have to do this everyday not surprising)
• Land Mine Removal gear (invention doesn't even hurt the environment although it takes solid rocket fuel)
• better Fire-Resistant Reinforcement for all building materials (invention stuff to coat steel and fire extinguishing expanding foam.)
• almost all Firefighter Gear uses their metal they created (invention)
• Temper Foam (that stuff you see in airplane seats and amusement park rides that protects your head invention)
• Baby food enrichment (invention was used for astronauts first.)

I will stop here and I haven't even gone deep into computer software food and water purification. (source)

How is exploring space helpful to us?

Well apart from the tech created above it is helpful and necessary in many ways.

Without colonizing other planets we will die.

Our planet has an expiration date. The sun will expand and consume us in a few billion years while many other things could wipe us out at any time. An asteroid impact could kill us all right now, but people on mars would be safe. Some things like black holes we have no chance of stopping. We need somewhere to go and to be spread out or we will simply die one way or another.

How can NASA save us here?

Well as mentioned above an asteroid impact could kill us all. NASA has the ability to track most asteroids and predict their path. This means that we will know if one will likely hit us or not and we can move it out of the way. They need the funding to have enough technology made and ready by that time and you can't do it at the last minute.

We are are running out of resources here on earth that are (more) common in space.

For example on the moon has a large amount of Titania (which we really need) and the rocks of it have 10x as much as here on earth. Mining would be far more efficient and profitable. ( source ) or asteroids filled with rare earth metals. We need rare earth elements to produce electronics and once we run out we will be crippled.

What about spaceX?

Well spaceX is a good company and is trying to do good things, but they still need to make a profit to operate. Being forced to operate at a profit stifles innovation of an organization just trying to explore space and create new things. Creating things to see what you can make and learn makes better things than be forced to operate for profit. Almost all modern advances in science are because of people wanting to learn more, not those trying to get money. (Sadly the ones trying to get money must advertise and get their name out their for money and are noticed more rip Nikolai Tesla.)

(also since nasa is in full public domain I only need to say I got them from NASA no link needed hahahahah)
nah jk here they are anyway: www.nasa.gov/sites/default/files/images/nasaLogo-570x450.png
neo.jpl.nasa.gov/images/ida1.jpg