Can worker cooperatives possibly be the foundation for socialism, given that the most modern historical efforts such as the Israeli Kibbutzim have failed or become capitalist corporations? The idea might be called Utopian.
I can live with the charge of utopianism. The left could use a bit more utopianism, since too much of that important "vision thing" got wrung out of too much of the organized left. Engels' critique of utopian socialism never intended to expunge the utopianism from socialism; his criticism rather overemphasized the "scientific" in order to get what he thought (and I agree) would be a better balance. And that is what I aim at now, in the reverse direction.
You are probably right that I need to be more careful to avoid sounding as though I think worker's self-directed producer collectives/cooperatives are "the" answer (what you refer to as “the foundation for socialism”). I agree that without other changes - e.g., socialization of means of production, planning, etc. - such coops alone will revert to capitalism much as you describe the kibbutzim. But, again, the reverse holds as well. Without collectivizing enterprises at the base of a socialist society - and that is not achieved by substituting state officials/commissars for private capitalist boards of directors - the socialization of property and planning too will revert to capitalism as happened in the USSR etc.
The trick that has so far eluded socialist experiments - notwithstanding their many achievements which I see and applaud - is the combination of macro-level socialist change with micro-level change of the sort I stress.