Would US states turn state militia guns on protesters?

The simple answer is yes. The US is going through a wrenching loss of prestige globally and is experiencing great economic pain, owing to the deep recession its finance capitalists visited not only on the US but the world at large.
The country is running huge deficits from which a military industrial complex draws immense benefits. It imposes on its 50 states a draconian provision that demands balanced budgets whilst Congress has shifted, notably since the presidency of the much hallowed and beatified Reagan, heavy burdens which the federal government should be carrying--all of which benefits a bloated, braindead plutocracy.
Right now, the eyes of the country are focussed on the state of Wisconsin. There, the newly elected Republic governor Scott Walker is proposing to deny state workers to bargain or strike for their rights, and with a dash of radical action, break and abolish employee unions. And what's more, should he force through a law forbidding state workers to protest publicly, he would turn the state militia on them. Wisconsin has a long radical tradition. It is the state of Robert LaFollette, a Republican and a Progressive, as well as a former governor, who opposed trusts, bossism, and America's entry into world war one. It has a strong tradition of industrial action and labour unions. On the other hand, Wisconsin sent 'Machine Gunner' Joseph McCarthy who is former associated with America's witch hunt during the 1950s and attack of constitutional liberties.
The 2010 US mid term elections brought to office on all levels of government -- municipal, state, and federal -- a strong group of Republicans who hidding behind the cover of the need for living within one's means and creating much needed jobs, came into office with a radical agenda favouring the rich and feathering their own nests.
Scott Walker belongs to such a breed of Republicans who attack the middle class, the working poor, and the marginal, in favour of the fat cats. His solution to difficult and almost intractable economic and social programmes is to crush any dissent by the use of force.
States have borrowed beyond their means, and the central government shares much of the blame. They have to cover yawning gaps of us$ billions to balance the budget that is mandated by law. Fellow Republicans who have a strong presence in the lower house of Congress, which hold the purse, won't help governors like Scott Walker. And fiscally conservative, he, might not want them to do so.
Consequently, to slash and burn, Walker is picking a fight with unions and has awakened the old 'progressive' spirit Wisconsin was once famous for. He is counting on pushing his proposal through the state legislature by hell or high water. Should he succeed, there are at least 11 Republican governors who share his views, ready to crush unionised state employees.
Although Walker may be concerned with the state budget, he is ideologically motivated by an extreme right wing ideology which not only deeply mistrusts the people -- and remember the US prides itself on being a government of, by, and for the people -- but who are the lackeys of a crude plutocracy who live high on the public hog whilsts the ratepayers slump into poverty and a Dickens' like existence.
Thus, in grosso modo, what's happening in Wisconsin is crucial to the rights of the workers to bargain collectively for a living wage and a decent standard of living for them and their children, and not to enrich the fat accounts of finance capitalists and their hanger ons.