I'm not sure how this works, actually - in my first BNW game I was suffering (mild) unhappiness from Ventian ideology despite having a higher tourism output per turn, however my influence (tourism vs. culture) was lower.
So it seems that culture is what defends against ideological tourism, in the same way as it defends against cultural victory. Tourism has no effect.
Not true
Ideological pressure from someone is calculated like this
Their level of influence with you - your level of influence with them
Unknown=0
Exotic=1
Familiar=2
Popular=3
Influential=4
Dominant=5
So if they are Popular against you (4), and you are Unknown to them (0).. then that is 4 "points" (4-0)
However, if you pump out a little bit ouf tourism (enough to get 10% against them),,They are still Popular (4), but you are Exotic (1).. then that is only 3 "points" (4-1)
That means that the way to reduce Ideological pressure is
1) increase your culture->decreases their influence with you
2) increase your tourism->increases your influence with them
And if Ideological Pressure from civs with Different Ideologies is more than that of civs with the Same Ideology... then you get unhappiness
As for the "build guilds get free stuff"... you realize that
1. you can spend policies to increase that amount of free stuff
2. you can pass resolutions that increase the amount of free stuff at the cost of other great persons
3. you can spend policies and faith to Buy that free stuff
4. you can spend to get archaeologists
5. those specialists could be doing something "useful"
6. some extra free stuff can be obtained by investing in world wonders
The Guilds do allow you to get some Baseline tourism for 'free'.. but there are significant 'toggles' if you want cultural victory (or to prevent one)