Should /l/ sound be always pronounced completely?

Solution 1:

The question is not should it always be pronounced completely but is it always. The answer to the latter is no.

Many native speakers of English have trouble producing that sound reliably. Variations of this symptom range from a "w" sound ("Don't be siwwy!") to a kind of swallowed consonant which is produced without the tongue ever touching the palate. Not only is this unremarkable, but one of America's most famous network television news anchors, Tom Brokaw, made it part of his onscreen personality. Listen to how he says "British Co[l]umbia" in this YouTube clip.

If you get close to the sound, people will understand what you're saying.

Solution 2:

I agree with Robusto about 'should'. There can be no prescription on this.

Cruttenden (Gimson's Pronunciation of English, 2001.203) notes that "In some speech, notably that of London and the surrounding areas, the tongue-tip contact for [ɫ] is omitted, this allophone of /l/ being realised as a vowel (vocoid) in the region of [ö] with weak lip-rounding or as [ɤ] with neutral or weakly spread lips.

[my emphasis added]