Friar Laurence can certainly be viewed as a good character because he has good intentions; although, for a Franciscan monk and priest, he certainly is a very complex character. As a result of his complex nature, he makes some poor choices that, sadly, help contribute to the play's tragic end.
We see evidence of Friar Laurence's good intentions all throughout the play. One example is seen in how he acts as mentor to Romeo. In fact, he and Romeo have such a strong father-son-like relationship that Romeo goes to him for counsel about his heartache over Rosaline and even runs to him with his happy news concerning Juliet. Although Friar Laurence thinks that Romeo is far too young still to really know what love is, he agrees to marry the couple because he sees it as an opportunity to unite the two feuding families, as we see in his lines:
In one respect I'll thy assistant be;
For this alliance may so happy prove
To turn your household's rancour to pure love. (II.iii.93-95)
Since Friar Laurence marries the couple with the sole intention of restoring peace in Verona, we see that he certainly is well-intentioned and can be considered a good character.
However, Friar Laurence's complexity first shows up when we see him out at dawn gathering both healing herbs and poisons. It was not uncommon for monks or priests to be knowledgeable in the healing arts of herbs. For centuries, monks practiced gathering and using herbs for medicine. The practice both developed and faltered as time progressed; nevertheless, books have been compiled of healing remedies known in the 16th Century and earlier. However, while gathering healing herbs may not have been unusual, gathering poisons as well is certainly a little unexpected. It is also extremely unusual for a monk to be able to make a poison that can make a person look dead for 42 hours. This unexpected part of his nature also seems to correlate with the part of his nature that can be seen as deceptive. While he had good intentions, it was deceptive of Friar Laurence to marry the couple in secret. In addition, it was certainly deceptive of him to help Juliet fake her death. It's the decisions he makes using the deceptive part of his nature that wreak havoc. Even though he had good intentions, he failed in accomplishing what he set out to accomplish in terms of peace because all of his plans went awry, leading to unexpected death instead. However, while his poor decisions play a role in Romeo's and Juliet's deaths, he is not ultimately responsible. Had the hatred between the Capulets and Montagues not existed, his marrying the couple would not have resulted in death.
Therefore, even though Friar Laurence makes some poor decisions and has a deceptive nature, he is ultimately a well-intentioned and good character.