Most people believe most things because they are well accepted by those who study it - and absent evidence of real, pervasive, academic misconduct in the field, that's what they should do. This applies to science as well - even though it is built on the premise that anyone could, in theory, test any hypothesis for themselves - in practice, basically no one ever does.
Expertise is rare, and relying on your own inexpert opinions and amateur research is an easy way to be wrong. This is even more important when you have a preference for one side or the other - I want Jesus to be a made up mythical figure because religions are so ridiculous - and I could pretty easily cherry pick facts to support that. But that way is a path to the Dark side, to conspiracy theories and tin foil hats.
I try to be better than the climate change deniers, flat earthers, and vaccine/autism link proponents. If that means accepting that there was a real preacher called Jesus who live 2000 years ago and got crucified, so be it.
Do you believe in abiogenesis and evolution?
What about electrons?
What's your criteria for believing in something to be true?
Before it's reasonable to believe that something actually exists (or existed), first we must define what qualifies. Abiogenesis, evolution and electrons are clearly defined things. But 'Historical Jesus' is not - that entity has many different definitions, and often more than one within a single argument.
If we define 'historical Jesus' as 'any person born in Bethlehem between 50BCE and 50CE to a carpenter's girlfriend, who went on to become a preacher, and was executed by the Roman authorities', then it's perfectly plausible that there was at least one 'historical Jesus'. But if that's our definition, then the real question becomes 'who gives a crap?'.
For it to matter a damn whether or not the 'Jesus' character actually existed, it seems to me that the character needs to be an accurate fit to a much more detailed and specific description - and that that description must:
A) be agreed upon by all participants in the debate; and
B) include at least a large fraction of the traditional biography of 'Jesus'; in particular
C) at the very least one, and preferably several of the supernatural claims, such as performing of miracles and returning from the dead.
Any character who meets these criteria is highly unlikely to have actually existed; any 'Jesus' who meets only less stringent criteria for recognition as the historical Jesus, simply falls into the 'So what' basket.
If there was an historical Jesus who was just some ordinary bastard son of a carpenter's girlfriend, then why would anyone care?
This is a major problem when discussing things with theists - they refuse to be pinned down to a set of firm definitions, and then equivocate like crazy - which apparently confuses them enough to make them think they have proven something, even if it's not fooling anyone else.
Nobody cares whether there was really a reporter called 'Clark Kent' working at the Daily Planet. Unless, that is, he was also able to leap tall buildings in a single bound.
Clark Kent's historicity is trivial - reporters are two a penny. Superman's historicity is a much more important question - but it's also much more easy to refute. Christians want to have it both ways - they want to say that as Clark Kent is a plausible candidate for having been a really real person, therefore Jesus the Christ is equally plausible. That's a logical fallacy (or a piss-weak attempt at fraud, if they are being disingenuous rather than merely stupid).