Allegations of racism any other 'ism' at work, at school, or in any social setting should be taken seriously and not automatically dismissed, but unfortunately there are those who make false allegations, either as a dishonest, deliberate tactical move to strengthen their bargaining position, or as an unconscious, reflexive reaction to baggage from past, unrelated experiences with prejudice.
In either case, the effect is ultimately negative for all involved. In the former situation, in which someone consciously wields the race card while knowing it is not warranted, a lack of trust results, and the credibility of future, legitimate complainants is damaged because of the selfish, short-sighted tactics of one individual. In the latter situation, the complainant is blinded by mind-made stories based on past experience (which may not be relevant in a particular situation) and fails to take responsibility for his or her own part in creating an undesirable situation. As a result, s/he is not able to take the measures needed to change his/her situation for the better.