Praise be to Allah.
So long as a Muslim is following the correct evidence (daleel) and has the desire to follow the Sunnah properly, there is no harm in following any of the Imams when it comes to rules of fiqh. In the case of the ordinary Muslim (who is not educated in fiqh), his madhhab (school of thought) is that of the mufti whose knowledge he trusts. But problems of the worst type occur when people become fanatically devoted to one particular imam or madhhab, to the extent that they reject the truth or ignore other sound evidence because of this.
Allaah warns against rejecting the word of the Prophet (peace and blessings of Allaah be upon him) (interpretation of the meaning): And let those who oppose the Messengers commandment (i.e., his Sunnah) (among the sects) beware, lest some fitnah (disbelief, trials, afflictions, etc.) befall them or a painful torment be inflicted on them. [al-Noor 24:63]
And Allaah is the source of strength.