I have always been the kind of liberal who believes in total artistic and intellectual freedom and the self-evident value of free cultural exchange – even naïve enough to think art and politics don't, and shouldn't, mix.

Yet I was glad to join other Scottish artists and writers in signing a letter protesting the appearance of the Israeli Batsheva Dance Company at the Edinburgh International Festival this week. Why? Because I have been profoundly changed by what I witnessed and experienced first hand during a short trip with a few student friends and some other poets and singers to Palestine this June.

We started off staying for a few nights as guests in Aida Camp in Bethlehem. This meant-to-be-temporary refugee camp of about 4000 people, some 650or so families, is exactly as old as me (and I'm 64) – having been established under a terrified flurry of canvas tents in 1948 as the grandparents and parents of the present generation either fled for their lives or were, at best, forcibly displaced from their homes and villages as the State of Israel was created.

Now it is a permanent, overcrowded, ramshackle, ad-hoc, self-build housing-scheme with wee creative and personal decorative motifs here and there, a mural, a fancy finial, ever-vertically expanding to accommodate its ever-expanding population.

The site occupies a far, far too small, finite geographical area bounded on one side by a lavish, brand new, Israeli four-star hotel complex, in the new international brutalist architecture style, and on the others by the observation towers of the Israeli Defence Force, built right into the camp's boundary walls. Bored young Israeli conscripts with very big guns look down on the Aida street life just a few feet below them.

Just-out-of-school weans playing with their pet cats, climbing in and out of skips and rubble, somebody running home at dinnertime with a tower of sandwiches hot and fragrant from the falafel shop, the young men hunkered and smoking, laughing and talking and sharing banter with the wee crowds of girls passing in their bright jeans and tight T-shirts – and, usually, though not always, the hijab headscarf.

These girls, studying for engineering degrees, some of them, came along to the "writing workshop" in the UNRWA-funded [United Nations Relief and Works Agency for Palestine Refugees] Lajee Centre that we tried to run, and were keenest of all that we should "tell the world we are not terrorists".

No shower for four days, just a rub down with baby wipes, as the water, stored in the tanks on the roofs, had just about run out again. A quotidian privation that most inhabitants just shrugged over. The Israelis turn on the water about once every three weeks, but randomly. Ach, they'd probably turn it on again in a day or two.

We were going on to a back-packers hostel in East Jerusalem. None of our Aida camp hosts, none of our new friends, could go to Jerusalem – only a little over five miles away. Their identity papers confine them to the West Bank. Oh, they tried to explain to me about the Green Line, the different classes of travel papers -

The petty daily debilitating harassments the Palestinians endure, as well as the huge historical injustice of the Nakba, the catastrophe, are hard to imagine unless you witness the effects of them first hand.

I can't say which incident in that crowded nine days turned me into someone who feels that we must use all possible means, all the time, always, of bringing the attention of our world to the Israeli apartheid, for that is what it is – to the appalling and illegal actions of Israel. The Wall. The settlements.

And I am fairly certain that most ordinary and decent Israelis don't know very much about what actually goes on, so poisoned has the narrative been, so separated are the two cultures.

Israel denies human rights to Palestinians. Denies that they are human beings at all.

Was it "a wee thing" like the arrogance of the soldier demanding the passports at Kalandia Checkpoint; or the heart-breaking testimony of the man in the tent in the desert with his thin sheep and scrawny goats in the burning stones of the Jordan Valley who had endured two house demolitions, rebuilt and resisted, and resisted – but was giving up and moving to the ghetto of the nearby "city" because the Israelis were disrupting the service of the school bus every other day, and he just couldn't bear to see his children deprived of an education?

Or was it witnessing the tear gas and the rubber bullets (no "skunk water" and only one live round that day, thank goodness) of the IDF at the weekly Friday, post-prayers peaceful Demonstration Against The Wall in the olive-growing village of Ni'lin?

Was it the bullet-holes in the lintels of The House of Poetry in Ramallah?

We must use all means. Including protesting at a dance company. Including total cultural and academic boycott.