> There's debate though if far-infrared was worth it though.

I don't think there's debate about whether the far-infrared is valuable. The far-infrared has unique diagnostic power for some astrophysical phenomena, and the 2020 Decadal Survey for Astronomy specifically called for the far-infrared to be considered for a $1B "probe-class" mission. What was debated was the specific role and cost of SOFIA.