Here is a brief comparison between Online and Land-Based Gambling.
These comparisons are provided to highlight the illogicality in targeting online gambling and are not a prescription to harm the land-based industry in any way.

Share of the market.

Annual Gambling Revenues Worldwide are $3000 Billion. Annual Online Gambling Revenues are $1 Billion.
So online gambling represents one thirtieth of one percent or one three-thousandth of the total gambling market worldwide.
If legislators really believe that gambling causes social problems, they should attempt to prohibit established land based gambling before online gambling. We would not in any way support such action but simply point to the hypocrisy involved.

Underage Gambling

Land based casinos often have to rely on appearance. So a mature young girl in high heels might be admitted, Online casinos however have instant access to data.
Credit cards are only issued to adults. Where there are children's cards they are so designated.
To this day none of the prohibitionists have provided a single example of underage online gambling or instances of fraudulent credit card usage by children. All the arguments are emotional and groundless.

Problem & Addicted Gamblers

Land-based casinos have very limited means to detect and deter problem gamblers.
Online casinos have a vast array of electronic possibilities. Shared databases, electronic barring, input by problem gambler or his family etc.

Money Laundering

It is more difficult for landbased casinos to check. Cash is cash.
To launder money at online casinos is much more difficult. Repayments are made to the credit card and winnings to the bank account of the player. Payments are more easily traced.
That leaves only the handful of operators who could launder money, as could the owners of terrestrial casinos or any other business for that matter. Deal with those people, not prohibit the entire industry.

Affects the Poor

Land based gambling, especially State Lotteries, Bingo, Football Pools and Horse Racing reach to every home and the very poor and uneducated.
Online gambling is generally a pastime for computer literate gamblers who tend to be generally more affluent and educated.

Poor Odds / Online casinos fairness

Land based casinos have high fixed costs to operate the casino as well as additional residential, entertainment and dining facilities in many cases. This limits their ability to compete on odds.
Online casinos on the other hand have low fixed costs and compete strenuously by way of promotions, introductory offers, incentives, better conditions etc.. Gamblers have never had it so good.

Honesty of Games

Software of online casinos can be constantly monitored by independent companies. Such operations are developing and are providing their services.

Ease of Access

It is true that it is easier to access an online casino
But it is also easier to leave the online casino. A click of the button and you're gone.
Visiting a land-based casino on the other hand is a different experience. It often involves a trip sometimes long distances. Once at the casino, having travelled, booked a room etc it is not easy to leave when you should.

So why pick on Online Casinos?

If Governments were serious about eliminating the perceived effects of gambling, they would logically also be seeking to prohibit land based casinos, lotteries, bingo halls, sports betting, horse racing and dog racing.
In addition to turning online operators into criminals, they should logically be incarcerating the hotel magnates for running casinos, bureaucrats for conducting lotteries, ministers of religion for running bingo sessions and so on.
Instead they pick on the small defenceless group of hardworking online operators, claiming that this will somehow cure all ills.
And they are supported by the bureaucrats, ministers of religion etc.

What is the reason?

Very simple:
Taxation and Control.
Anything they can't tax or control they try to prohibit.
And use false arguments to justify it.