The English-speaking world may be divided into (1) those who neither know nor care what a split infinitive is; (2) those who do not know, but care very much; (3) those who know & condemn; (4) those who know & approve; & (5) those who know and distinguish.
The sixth camp correctly holds that infinitives in English cannot be split, ergo there is really no such thing as a split infinitive. For some reason, we have been told that the infinitive in English includes the prefix "to," but there is actually no reason to accept that description.
- I could prove it if I wanted to.
- But I don't have to.
- And I'm not going to.
The opposite of sentence 2 above, for instance, could easily be 4a, but not 4b:
4b. *I have.
It follows that we no longer need to speak of "bare infinitives" with modal verbs (such as 4a) at all. Occam's Razor holds that the simplest explanation is the best, and I have just demonstrated that the insistence that infinitive verbs in English include "to" brings about such unnecessary things as split infinitives and bare infinitives in the first place.
Since English is actually far more closely related to modern German than to Latin, a comparison of how infinitive clauses work in the two languages is also illustrative:
5. I helped him to cross the street.
6. Ich half ihm, die Strasse zu überqueren.
Notice that, although German never considers the infinitive to include "zu" (which is essentially equivalent to the English "to") and it does not even have the concept of split infinitives (the German Wikipedia entry for split infinitives discusses the issue as a problem affecting English and gives the example of "to boldly go" from Star Trek), no native German speaker would ever be able to put any word between "zu" and "überqueren":
7. I helped him to safely cross the street.
8. I helped him to cross the street safely.
9. Ich half ihm, die Strasse sicher zu überqueren.
10. *Ich half ihm, die Strasse zu sicher überqueren.
To my taste, this comparison clearly shows that the German language does not have a history of stupid grammarians going around making up rules to ban things that feel right for all native speakers because you couldn't translate the construction into Latin (though you certainly can translate the meaning). In contrast, English has a number of rules -- split infinitives being only one -- that would rule out things that sound perfectly fine to all native speakers. Even after generations of attempts to stamp out split infinitives, all native speakers -- including those who say that split infinitives do not sound good -- continue to use them when they sound right, the opponents merely doing so only when they let their guard down.
Granted, I personally like sentence 8 above more than sentence 7, but there are slews of examples where the supposed split infinitives actually sounds best to me -- "to boldly go" being one good example.