Tl; dr: In most cases the past tense is not wrong. The present tense is only correct if the statement is indeed still true.
The somewhat subtle difference is that the simple "would require" indicates that this requirement or possible route not chosen is still existing or possible at the time of speaking. For example, imagine a press conference about an ongoing hostage situation:
We decided against a police intervention because the risk for the hostages would be unacceptably high.
At the time of speaking, the risk still would be too high. One could use the past tense here as well, avoiding a statement about the present:
We decided against an intervention when the group entered the building because the risk for the hostages would have been unacceptably high. But our snipers are still in place and we are monitoring the situation closely.
But the present tense cannot be used for requirements or possibilities which do not exist any longer. In a report about the same situation a year later, one might read:
We decided against a police intervention at this point because the risk for the hostages would have been unacceptably high.
In this case, the present tense would be wrong because the risk does no longer exist.
I suppose that in scientific articles the present tense is often adequate because the requirement is still there:
We did not check for specific compounds in the samples because the small concentrations would require specialized analytical equipment.
They still do.