Yet another one of those Canvas navigation requests. In most other DCC s/w by default LMB+drag will select rather than pan in the graphs. Check Blender, Houdini etc. Which I find more intuitive as most apps have panning bound to MMB instead.
Wonder if this can be a config option in settings perhaps? It is hard to learn new input method esp when you keep bouncing all day long between different apps.
As for the use of Alt. I think the main reason Houdini and Co use Alt+mouse buttons for navigation rather than just mouse buttons is to leave normal LMB/MMB/RMB for other actions which are context dependent. e.g. LMB = click select, LMB+drag = box select, RMB = context menu etc.