Is befriending and reconciling with someone who was advised against committing a forbidden act and was spoken to harshly for it blameworthy, or is it a deficiency from what is more perfect?

The strictness is subject to what serves the best interest, so leniency is sometimes more appropriate. One must be wary of strictness motivated by personal inclination. Imam Ahmad and Abu Dawud narrated the story of the worshipper who became angry for the sake of Allah and said to a sinner: "By Allah, Allah will not forgive you." So, Allah forgave the sinner and nullified the worshipper's deeds, because he spoke improperly and presumed to dictate to Allah. As for the one who commits a sin or abandons it: if he repents, then "the one who repents from sin is like one who has no sin," and he should be given the rights of a Muslim. If he does not repent, then it is permissible to shun him if that would deter him; otherwise, there is no benefit in shunning.