Which is correct in both meaning and grammar, 'argue' or 'to argue'?

Which is correct in both meaning and grammar, 'argue' or 'to argue'?

1. As a general rule, historians find it difficult to isolate events in history and argue their impact upon society. [bare-infinitive parallelism]
2. As a general rule, historians find it difficult to isolate events in history and to argue their impact upon society. [to-infinitive parallelism]

Is there no difference in meaning between the two sentences?

In my opinion,

1. to (isolate ... and argue ...) : subsequent acts

2. (to isolate ...) and (to argue ...) : separate acts

Thus, I think that 'argue' is a logically correct expression.

When repeating parallel structures it's often permissible to omit repeated words, without changing the meaning in any way.

When driving in the UK, American drivers must learn to stay to the left, (to) follow all road signs, and (to) watch out for cross-traffic.

In an emergency keep calm, (keep) organized, and (keep) alert.

Retaining the repeating words can add emphasis to that specific action:

The only way to get control of your life is to turn off the phone, turn off the TV, turn off the computer -- and turn on to what's happening around you in the real world.