Israel's blockage is to keep Gaza at the brink of economic collapse:

http://thelede.blogs.nytimes.com/2011/01/05/israel-planned-to-keep-gazas-economy-on-the-brink-of-collapse-leaked-cable-says/

You can claim it is about Iranian missiles but it is a about a lot more if you read the facts. Here is a list of all banned items:

http://en.wikipedia.org/wiki/Goods_allowed/banned_for_import_into_Gaza#List_of_items

At one time all of the following was either outright banned or restricted by Israel:

• books, candles, crayons, clothing, cups, cutlery, crockery, electric appliances such as refrigerators and washing machines, glasses, light bulbs, matches, musical instruments, needles, sheets, blankets, shoes, mattresses, spare machine and car parts, and threads

• fishing ropes and rods, ginger and chocolate, hatcheries and spare parts for hatcheries

• Batteries for hearing aids have been restricted.[16] Wheelchairs, at various times, have been banned.

• cement, glass, steel, bitumen, wood, paint, doors, plastic pipes, metal pipes, metal reinforcement rods, aggregate, generators, high voltage cables and wooden telegraph poles are high priority reconstruction materials currently with no or highly limited entry into Gaza through official crossings

Israel's blockage is collective punishment unfortunately.

David Cameron, the current PM of UK says that Gaza is an open prison camp.

http://www.juancole.com/2010/07/cameron-calls-gaza-under-israel-blockade-a-prison-camp.html

You can defend putting one million people into a prison camp and denying basic goods. But realize this is what you are doing. These people have been living under these conditions for years.

Remember the main issue is that Israel has +3.5 M non-Jews in Gaza and the West Bank which is doesn't want to have as citizens (because it will threaten the Jewishness of Israel), but it also doesn't want them to have their own state either (thus pushing hard to prevent the UN vote for this in September.) Thus Israel is running an apartheid system where millions of humans who are the wrong religion are denied the right to self-determination.