I can't think of any historian who would be generous enough to Baldwin to give him a motivation other than seeing an opportunity to gain power and influence.* That said, the degree to which his actions and motivations are seen as despicable varies from author to author. Baldwin was a younger son, and so had no prospect to inherit back in Europe, so it's somewhat logical that he would try to gain control of lands while in the Holy Land. In fact, his status as a younger son, along with his eventual success at taking power, was a major contributing factor to the development of the myth of crusaders being mostly younger sons.

That having been said, there's not necessarily anything inherently wrong with his seeking land. That was the done thing at the time, what makes Baldwin so novel is how far from home he was when he did it. Thoros of Edessa, meanwhile, seems to have not had any heirs of his own, and was in a very precarious position. Edessa is pretty far out on its own (a problem that contributed significantly to its status as the first Crusader State to fall), and Thoros does not seem to have been very popular. Calling for Crusader help was his best bet to keep his land independent, and Baldwin an ideal candidate for helping him. Thoros eventual death at the hands of his own people has caused endless speculation about whether Baldwin was behind it. There's not a lot of hard evidence to go on here, so while it's certainly possible, it is by no means definitive.

Peter Frankopan has recently argued that instead of establishing his own county, Baldwin was taking control of a Byzantine territory, and even took on Byzantine titles and attire in his new role. This would suggest a version where Baldwin positioned himself to inherit the county. Baldwin's decision to travel to Edessa is still generally seen as one of self-promotion first, the idea that he would travel their primarily out of a selfless desire to aid the county and its ruler is not a particularly strong one (he had no connection to either).

That Baldwin's independent campaign ended up being of great assistance to the overall Crusade has generally been accepted. The most concrete example of his assistance came during the siege of Antioch. The atabeg of Mosul, Kerbogha, stopped on his way to Antioch to besiege Edessa. This siege lasted some time (I believe 2 weeks, but I don't have my books on hand), and was ultimately unsuccessful. However, during his siege of Edessa, the Crusaders succeeded in taking Antioch, thus saving themselves from being trapped outside the city when Kerbogha arrived.

The fact that Baldwin did not participate in either the Siege of Antioch or the campaign to Jerusalem has earned him some scorn over the centuries. However, he's hardly unique in his absence from Jerusalem (Bohemond, infamously, did not journey beyond Antioch).

*I don't have my copy of Fulcher of Chartres on hand, but he may have excuses for Baldwin's departure from the main Crusade. He accompanied Baldwin to Edessa, and was generally his #1 fan, at least as far as chroniclers go.

Asbridge's The Crusades is pretty representative of the general outlook on Baldwin's departure, at least right now.

Peter Frankopan's The First Crusade: The Call from the East has information on it from the perspective of Byzantium/Edessa, which presents an interesting alternative look.