Whatever you think of Trump's proposed Space Force, it has at least one ally in its corner: recently-installed (and Trump-selected) NASA administrator Jim Bridenstine. In an interview with Axios, Bridenstine argued that space was becoming "more contested" and that the US had to be "willing to defend" space in order to maintain it. He argued that the Chinese and Russians were developing not only anti-satellite missiles, but co-orbital satellite weapons, jammers and other spaceborne threats. Allegedly, the Chinese see the US' lack of space weapons as an "Achilles' heel" it could exploit.
Bridenstine stressed that the Pentagon would be responsible for the Space Force if it goes forward. He just supported the notion of a unit that protects astronauts and the "billion-dollar-plus investments" they're using.
There is a degree of truth to the concern in that other countries have been developing anti-satellite weaponry for years -- it's not as if they're going to stop. It's not certain that these countries intend to attack or disable US space assets, though, and there's a worry that the Space Force would lead to a militarization of space that people have sought to avoid for decades. As it is, the NASA administrator's voice only carries so much weight -- it's ultimately up to the Pentagon to decide if a Space Force is viable.