Roosevelt signed an alliance with Stalin. Reagan traded arms with Iran.
Presidents cut shady deals thinking its best for our country. How it works.
Of corse, a deal with a Mexican cartel (fast and furious) or Islamic extremists seems a bit nutty.
Oh wait. We armed the anti soviet Taliban.
The Taliban did not come about as a force for fighting the Soviets, but much later, in the aftermath of the war, in much the same way as the mafia takes over urban areas where crime has become so rampant that people look to anyone to restore some form of order. The mafia "helps" by providing locals with desirable skills or assets a number which they can call if they need help. Woe to anyone who calls it. They will get help but it comes with an everlasting obligation to pay protection money, or to provide services illegally. In the case of the Taliban, they appeared in the form of "students" and "youths" led by old Mullah Omar in the outlying regions during the period the new post-Soviet government, having just ousted the last Soviet puppet, was trying to get on its feet in Kabul. (Its defense minister was Shah Ahmed Massood- and Massood was the guy to whom our aid, stingers, and such had flowed. He was the guy al Qaeda, by then hosted by the Taliban, had assassinated on Sept 9, 2011.) Of course what the Taliban were really doing was winning the hearts of locals by toppling the weaker warlords and taking their territory and business for themselves, developing a monopoly on opium.
The new government had a pretty good grip on Kabul but was wobbly because of the presence of Gulbuddin Hekmatyar, who was the apparent favorite of the pro-Pakistan folks in the state dept as a "stronger horse" than Massood. But Pakistan was determined to destabilize the new government further out of fear it might have relations with India. Pakistan discovered the Taliban as they were forming and noted they were initially very popular in areas where there was as yet no law enforcement or army, and chose to provide them with vehicles, funds and weapons, using them to gain control of Afghanistan's roads, such as they were.
Gulbuddin Hekmatyar as we know later joined up with al Qaeda. Now, al Qaeda had been around since 1988, older than the taliban, but in its early stages was based in Pakistan, Sudan and finally in 1996 Afghanistan. It formed out of MAK, Azzam's organization, after OBL got in a spat with Azzam and Azzam turned up dead.