Men shall be fierce in the last days.
Matthew 11:29 King James Version Take my yoke upon you, and learn of me; for I am meek and lowly in heart: and ye shall find rest unto your souls. (Matthew 11:29 [KJV])
We should take Jesus yoke upon us and be meek which is the opposite of fierce.
To have fellowship with fierce Christians can be perilous because its supposedly fellowship in Christ but Christ is meek and lowly in heart and they are the opposite to Christs meekness. So on a spiritual level it can be detrimental to have fellowship with them.
 This know also, that in the last days perilous times shall come.  For men shall be lovers of their own selves, covetous, boasters, proud, blasphemers, disobedient to parents, unthankful, unholy,  Without natural affection, trucebreakers, false accusers, incontinent, fierce, despisers of those that are good,  Traitors, heady, highminded, lovers of pleasures more than lovers of God;  Having a form of godliness, but denying the power thereof: from such turn away.  For of this sort are they which creep into houses, and lead captive silly women laden with sins, led away with divers lusts,  Ever learning, and never able to come to the knowledge of the truth.  Now as Jannes and Jambres withstood Moses, so do these also resist the truth: men of corrupt minds, reprobate concerning the faith.  But they shall proceed no further: for their folly shall be manifest unto all men, as theirs also was. (II Timothy 3:1-9 [KJV])
It is similar to
Make no friendship with an angry man; and with a furious man thou shalt not go: (Proverbs 22:24 [KJV])
Should we then have fellowship with someone that is fierce. Of course not. That is against the scripture.
How should we deal with fierce Christians ?
We should turn away form them.